Brigham Young University Geology Studies

YOUNG
' Volume 13 December 1966
I
CONTENTS
Thc~deLobmiadAssuciPted~s,Varw,~
J. Keith Rigby and Wdri G. M c W 3

Brigham Young University Geology Studies
Volume 13 - December 1966
Contents
The Isla de Lobos and Associated Reefs, Veracruz, Mexico
........................................... J. Keith Rigby and William G. McIntire 3
Some Octocorallia of Isla de Labos, Veracruz, Mexico
........................................................................... C. Kent Chamberlain 47
Dinosaur Eggs from the Upper Cretaceous North Horn Formation
of Central Utah ........................................................ James A. Jensen 55
Geology of the Kingsley Mining District, Elko County, Nevada
.................................................................................... Roger Steininger 69
A Study of Fluid Migration in Porous Media by Stereoscopic
Radiographic Techniques ................................ J. Raymond Rutledge 89
Actinocoelia maeandrina Finks, from the Kaibab Limestone of
Northern Arizona ........................................... Leland R. Griffin 105
Preliminary Petrology and Chemistry of the Cenozoic Basalts in the
Western Grand Canyon Region
.... Myron G. Best, Wm. Kenneth Hamblin, and Willis H. Brimhall 109
Publications and Maps of the Geology Department .................................... 125

A publication of the
Department of Geology
Brigham Young University
Provo. Utah 84601
Editor
J. Keith Rigby
Editorial Staff
Lehi F. Hintze Myron G. Best
Brxgham Youug University Geology Studies is published annually by the
department. Geology Studies consists of graduate student and staff research
in the department and occasional papers from other contributors, and is
the successor to B.Y.U. Research Studies, Geology Series, published in
separate numbers from 1954 to 1960.
Distributed February 20, 1967
Prxce $4.00

The Isla de Lobos and Associated Reefs, Veracruz, Mexico
J. KEITH RIGBY AND WILLIAM G. MC~NTIRE
Brigham Young University; Louisiana Slde University
ABSTRACT.-T~~ reef which surrounds Isla de Lobs is one of three closely associated
reefs on the eastern coast of Mexico, approximately 70 miles southeast of Tampico,
Tamaulipas, and is the northernmost reef with a sand cay on the western margin of the
Gulf of Mexlco. It rises from a detrital plain, with a depth of approximately 120 feet,
to near low tide, where the reef forms a flame-shaped lagoon approximately eight
thousand feat Img, north-south, and three thousand five hundred feet wide.
The island is situated in a shallow lagoon which has an average depth of less than
3 feet and a reef-formed margin which is barely awash at lowest tides. Leeward and
windward reefs can be differentiated topographically on fathograms and on the contour
map of the reef complex and adjacent areas. Leeward development is characterized by
broad, flat-bottomed, but steepwalled grooves, in contrast to more narrow V-shaped
grooves in windward development. The reef toe is flanked by calcareous, reef-derived
sand on all but the northeast side, where scattered data suggest a rocky floor.
Several lagoonal, reef, and surrounding deepwater habitats and communities can
be differentiated and were mapped, all seem closely related to substrate character.
Tbala~sia and Hdimeda blanket much of the lagoon and have trapped a stable sand sub
strate. These forms, along with Porites spp. and Diploria rliuosa, characterize stable
sand communities. Unstable sand communities are poorly developed and only locally
present, but infratidal lagmnal rocky-bottom habitats and communities are well developed,
even though cif limited areal extent. A rocky-shore habitat is present on hurricane-tossed
boulders and man-made structures, but rocky-shore communities are only
beginning to populate the area because the habitat has been only recently opened.
An algal ridge forms the crest of both windward and leeward reefs and qarates
the marginal reef flat, Diploria rliuosa, and the more lagoonward, algal oncolite cornmunities
from seaward reef development. Both windward and leeward reefs are characterized
by an Arropora palmafa community in shallow water. In deeper water, from approximately
25 feet down to 50 or 55 feet, a Diploria strigosa community forms the
windward reef and a Montastrea annularis community forms the leeward reef. The
Montasfrea ravernosa community forms the basal 25 to 30 feet of both windward and
leeward reef development.
CONTENTS
TEXT
page
Introduction ........................................ 4
Circulation ........................................ 16
Turbidity ....................................... 19
Tides ............................................... 20
Location ........................................ 4
Access ................................................ 5
Personnel ......................................... 6
Methods of Study ............................ 6
Acknowledgments ............................ 9
Topography .......................................... 9
Jsla de Labs .................................... 10
Submarine topography .................... 10
Habitats and Communities .................. 20
The Rocky Shore ............................ 22
Rocky-Shore Habitat .................... 22
Rocky-Shore Communities .......... 23
The Sandy Shore .............................. 24
Sandy-Shore Habitat and
Community .............................. 24
The Lagoon ............................ . ...... 24
Lagoon ......................................... 11
Leeward Reef ................................ 11
Windward Reef ............................ 13
Southern Sand Apron .................. 15
Northwe;tem and Southwestern
Tongues of Sand .................... 15
Western Plain ............................ 16
Eastern Rocky Slope .................... 16
Hydrology .......................................... 16
Infratidal Rock-Bottom
Habitats .................................... 24
Infratidal Rock-Bottom
Communities ............................ 24
Unstable Sand Habitat ................ 25
Unstable Sand Community ........ 26
Stable Sand Habitats .................... 26
Stable Sand Communities ............ 26
Arenirola(?) Community ........ 26

4 J. K. RIGBY & W. G. McINTIRE
Thalassia-Halimeda
Community .......................... 26
Thalassia-Porites
Community .......................... 28
Thalassia-Diploria
Community 29
Lifhofhamniurn Gravel Habitat
and Community ........................ 29
The Reef .......................................... 30
Red Habitats ................................ 30
Reef Communities ........................ 30
Diploria clioosa Community .... 30
Lithothamn~um Ridge
Commun~ty .......................... 32
Acroporu palmafa Community.. 33
Montas/rea annularis
Community ............................ 34
Diploria sfrigosa Community .. 35
Mottfastrea ruvernosa
Comnlunity .......................... 36
North Channel Habitat
and Community .................... 38
complex at Isla de Lobos ........ 12
4. Fathograms of lateral traverses
in the leeward and windward
reef at Isla de Lobos ................ 14
5. Approximate current directions
and velocities in and adjacent
to the lagoon at Isla de
Lobs .......................................... 18
6. Substrates associated with the
reef at Isla de Lobos ................ 2 t
7. Topographic and community
profiles within the lagoon ........ 27
8. Topographic and community
profiles of windward and
leeward reefs at Isla de Lobos .. 31
9. Diagrammatic cross section of
the margin of the ship channel
showing possible zonation ........ 42
Plates
1. Topographic map of the reef
complex at Isla de Lobos
Dead and Channeled Area
of Reef ................................ 39
Surrounding Deep-Water Habitats
and Communities ........................ 41
Geologic History ................................ 41
Late Lagoonal History .................... 41
Blanquilla Reef .................................... 43
Leeward Reef .................................... 43
Lagoon ......................................... 44
Windward Red ................................ 45
Medio Reef ........................................ 45
References Cited .................................. 46
ILLUSTRATIONS
Text-figures
1. Index map ................................ 5
2. Map of fathometer traverses,
........................ in envelope at back
2. Community map of the reef
complex at Isla de Lobos
........................ in envelope at back
3. Boulder ridge, Thalassia flats,
and aerial views of Isla de
Lobos ................ following page 32
4. Underwater photographs of
lagoonal environments on Irla
de Lobs ........ following page 32
5. Underwater photographs of
lagoonal and marginal environments
on Isla de Lobos
........................ following page 32
6. Underwater photographs of
upper reef environments on
Isla de Lobos .... following page 32
7. Underwater photographs of reef
3.
sample traverses, and other
control points on the Isla de
Lobs reef complex .................. 7
Main topographic regions
associated with the reef
8.
environments on Isla de
Lobos ................ following page 32
Underwater photographs of
lower reef environments on Isla
de Lobos ........ following page 32
INTRODUCTION
Isla de Lobs is a smd sand cay which caps one of three small, but well-
defined, reefs along the eastern coast of Mexico (Text-fig. 1). These three
structures rise from the broad, shallow, detrital-blanketed shelf to near low
tide and are the northernmost such reefs along he western shore of the Gulf
of Mexico. Other smaller coralline structures are known to the north, but
usually in deeper water and of relatively limited scale. It is 'because of the
sand cay development and well-defined reef structure that Isla de Lobos reef
was selected as a base for the present study.
Location
Isla de Lobos is one of three similar reefs along a northwesterly tread,
southeast of Tarnpico, Tamaulipas, and southeast of Caba Rojo and Tamiahua

ISLA DE LOBOS REEF, MEXICO 5
TEXT-FIGURE 1.-Index map. The reef associated with Isla de Lobos was the major area
of investigation, but reconnaissance observations were also made on the associated
Blanquilla and Medio reefs.
Lagoon (Text-fig. 1). Isla de Lobs reef is the southeasternmost of the three
and is located approximately 7 miles off the mainland coast, 35 miles northeast
of Tuxpan, Veracmz, and 68 miles southeast of Tarnpico. The island on
the reef is located at approximately 21" 27' 15" North Latitude, and 97O 13'
45" West Longitude.
The island itself is a small sand cay, approximately two thousand feet
lone. one thousand feet wide. and with a maximum elevation of 11 or 12
0'
feet. It is, however, a most suitable base from which to study the surrounding
lagoon and reef, for from the small island most of the lagoonal and upper
reef regions are readily accessible even without using small boats. Development
of dock facilities by Pemex has also increased the ease of studying the surrounding
deeper water regions with small boats based on the island.
Access
Isla de Lobos is currently readily accessible via Pemex barges and tugs from
Tuxpan, 35 miles to the southwest. Since considerable petroleum is produced
from ehe well platform within the lagoon, daily round trips are made between
the dock on Isla de Lobos and the Barra de Tuxpan petroleum facilities east
of Tuxpan. Without Pemex cooperation, the only access to the island is by
small boat.

6 J. K. RIGBY & W. G. McINTIRE
Personnel
The authors were senior scientific investigators on the study, and were
ably assisted by C. Kent Chamberlain, a graduate student at Brigham Young
University; Rdolfo Cruz, a graduate student at the Instituto de Geologia at
University of Mexico; Rodney Adams and Norwood Rector, both on the staff of
Coastal Studies Institute at Louisiana State University.
McIn,tire was responsible for study of the island ecology, history, sediments,
etc., and Rigby was responsible for study of the reef and the lagoon.
Chamberlain studied the alcyonarians of the reef com lex and will publidh his
paper elsewhere. Adams and Rector were responsi le for equipment, and
logistics in general, and did most of the boat work for the party. In addition,
they did sediment sampling, along with Cruz, and Rector, In particular, took
many of the underwater photogra hs of the reef and bordering sand apron.
Marine organisms were iden,tiled by Rigby and Chamberlain, and subaerial
organisms were ~dentified by McIntire. Extensive collections were made as a
joint effort of all personnel and are housed at Br~gham Young University and
Louisiana State University.
Mapping was a joint effort of the whole crew. McIntire, Rector, and Adams
ran the fathometer traverses and carried the surveying rods in the island, reef,
and lagoon surveys. Rigby and Clmmberlain ran the surveying instruments,
plotted the points, and contoured the maps.
Methd of Study
Outline of the island, ship channel spoil heap, and well platform were
determined 'by plane table mapping at a scale of 500 feet per inch. Crest of the
reef around the relatively shallow lagoon was walked out and mapped at the
same scale from stations on the island margin, we11 platform, or within the
lagoon. A single station was established in the interior of the lagoon northwest
of the platform so that the northern tip of the reef was within instrumental
limits.
Once the outline of the reef and island was establ~shed, a series of fatho-
meter traverses were completed for topographic control within the reef and
adjacent deeper water. Locations of points on the fathometer trace were
established using a theodolite based in the top of the lighthouse at the southern
end of the island. Direction and distances were determined trigonometrically
since he elevation of the instrument was established slightly over 100 feet
above sea level, and orientation to known points could be established. Thus
vertical and horizontal angles would give the position of the boat at each
point necessary. Two-way radio allowed communication between the boat and
the lighthouse. Accuracy is greatest in Ehe southern half of the map where
angles were greatest, and least in the northern part where angles were lowest.
Fathometer traverses and control points are shown on Text-figure 2, along
with hallow-water traverses, sample stations, dredge stations, and deep dive
stations.
Shallow-water traverses were made using a knotted rope for distance, and
paired stakes for directional control. These traverses, coupled with low altitude
oblique photographs, were used in construction of the community map. Biologic
samples and sediment were collected during the traverses, and tied to distance
from shore.
g

lSLA DE LOBOS REEF, MEXICO 7
TEXT-FIGURE
2.-Map of fathometer traverses, sample traverses and other control points
on the Isla de Lobos reef complex. Fathometer traverses are shown as dashed lines
and shallow water sample traverses as dotted lines. Individual sample points and
deep dive localities are shown as numbered black circles.

8 J. K. RIGBY & W. G. McINTIRE
Several traverses were made of the lower part of the reef, from near the
toe upward, or from the sand apron upward. !hba gear was used with excellent
results for it allowed freedom of movement and sufficient time for study of
the deeper parts of the reef and surrounding sedimentary apron.
Sediment samples from pints not studied during deep dives were col-
lected with a clam-shell sampler. These include samples taken for living fora-
minlfera, micro-mollusks, and sediments around the flank of the reef and in
Che surrounding sand apron.
Notes on all underwater observations were taken on frosted plastic plates
with an ordinary lead pencil, transcribed at night, and then the plates were
erased ready for the next day's use.
Biologic collections were made using plastic buckets and inflated inner-
tubes, weighted wlth 1,ine and lead weights, on shallow traverses. Small speci-
mens were placed in plastic vials and larger specimens were placed in plastic
bags. Deeper water collecting was done with purse-like collecting bags instead
of the floating plastic buckets.
A water-soluble dye, Rodamine Red, was utilized in current velocity and
direction studies. The dye mixture is slightly heavier than sea water and sinks
gradually below the wave zone for determination of direction and velocity of
intermediate and bottom currents. Although it diffused somewhat in its course,
direction and velocity of motion were easily established.
Tidal information was not readily available for Isla de Lobs, although
some information is available for Tuxpan, to the southwest, and Tampico, to
the northwest. A tide gauge was established at the Pemex dock within the ship
channel and a continuous hourly observation record was maintained for 48
hours. In addition, a still-water gauge was established in the lagoon at the
south end of the island, but was read at somewhat irregular intervals.
The following is an approximation of crew-days spent in various types
of observation or preparation, calculated on two crews per day while we were
on the island.
Table I
Crew-days Spent in Various Activities During Observation of Isla de Lobos
Plane table mapping reef and island 10 days
Theodolite-fathometer mapping 4
Shallow water traverses G
Deep water traverses of reef 4
Deep water sediment samples 2
Current study and water chemistry 2
Helicopter flight 1
Logistics and support G
Island sediments and water study in pits 3
Study of spoil piles 1
Review of Blanquilla and Medio Reefs 2
Office work because of weather 4
Moving and sample preparation 3

1SL.A DE LOBOS REEF, MEXICO 9
Limited analyses of various water samples were undertaken using Hach
Engineer's hboratory, Model DR-EL, a p~able kit designed specifically for
water analysis. Chlorinity, salinity, F%, turbidity, hardness, and content of
oxygen, iron, lead, copper, cahnates, sulfates, silica, etc., can be determined
calorimetrically.
Acknowledgments
We are particularly grateful to Professor Guillermo P. Salas, Director of
the Instituto de Geologia at the University of Mexico, Mexico, F. D. Much
of the preliminary arrangements and attention to detail were accomplished
by him and his staff.
Assistance of personnel of Petrdeos Mexicanos is gratefully acknowledged.
Sr. Ing. Antonio Gracia Rojas and Sr. Ing. Eduardo J. Guzmln in Mexico City
arranged official permission to work on the island. Ing. Edmundo Cepeda and
Ing. Rodolfo Suarez, Tampico, were especially helpful in solving logistic prob-
lems while on the island; Sr. Alvaro Lorenzo, in charge of Pemex operations at
Tuxpan, and Sr. Juan Perez aided our study in many ways, and through their
kindness much of the Pemex facility was made available to us. Engineer Sr.
Inocencio Cadena was in charge on Isla de hbos and supplied us with ware-
house space and dock facilities, made certain that our personnel was housed,
and our groceries were transported from Tuxpan. We are also grateful for the
favors rendered by Capt. P. A. Carlos Mora Perez from Cerro Azul.
Appreciation is expressed to Mr. L. Lee Welch, Vincent and Welch Inc.,
Lake Charles, Louisiana, who allowed us to use his lodge for a base for the
first four weeks of our study. His caretaker, Sr. Santos Coronado, was also very
helpful and proved an excellent cook and fisherman.
- officials at the lighthouse on Isla de Lobos were also most kind. The
ancient keeper of the lighthouse, Sr. Papro Guzman, and his wife filled us in
on background of the island and its recent history. Sr. Roberto Caye Beeks and
his brother, Sr. Gregario Caye Beeks, both stationed at the lighthouse, were
also of considerable help, particularly since both were proficient with both
Spanish and English.
Mr. Norwood Rector, of Coastal Studies Institute at Louisiana State Uni-
versity, developed or modified considerable gear for the study. He was not only
responsible for the initial development, but also made repairs in the field. He
also supervised our somewhat amateurish diving and did much of the deep
water diving, collecting, and observation.
Study of the reef at Isla de Lobos was conducted through the Coastal
Studies Institute, Louisiana State University and supported financially by the
Geography Branch of the Office of Naval Research, contract Nonr 1575 (03),
NR 388 002.
TOPOGRAPHY
Isla de Lobos is a small sand cay in the interior of a broad shallow lagoon,
and is the northernmost sand island associated with reef development along the
western margin of the Gulf of Mexico. The reef is a flat-topped structure, but
with moderately intricate marginal topography, and shows the distinctive topo-
graphic expression of both windward and leeward development.

10 J. K. RIGBY & W. G. McINTIHE
Isla de Lobos
Isla de Lobos is built by calcareous sediment derlved from the surrounding
flat interior of the reef lagoon. The subaerial island is crescentic, somewhat
like the main reef, and is located in the southwestern part of the lagoon (Textfigs.
2, 3). It has an arcuate eastern coast and a nearly straight western one,
approximately 2100 feet long. It has a maximum width of approximately one
thousand feet near the mlddle of the broad arcuate eastern shoreline. The
island is a low feature, rlsing only to a maxlrnum of 11 to 12 feet above low
tide at the southern end of the island near the lighthouse. Elsewhere most of
the island 1s only 5 or 6 feet high.
A ship channel and associated spoll pile have been dredged through the leeward
or western lagoon to the northwest point of the island where dock facilities
have been established for Pernex operations. The ship channel, approximately
22 feet deep and 75 feet wide, was dredged 1500 feet long to the tip
of the ~sland, and then an additional 2400 feet northeastward through the
lagoon to a well slte platform near the windward edge of the reef. A road has
been constructed on top of the spoil pile on the windward edge of the shlp
channel. It is approxlmately 5 feet above low tide throughout ~ts len@h.
Narrow, but much hlgher heaps of spoil have been maintained on the leeward
edge of the s~hlp channel opposite the dock facilities and part of the well platform,
presumably as protection from the strong winds of the northwesterly
wlnter storms.
A concrete well platform, approximately 200 by 240 feet and 8 feet above
low tlde, was constructed in the east-central part of the lagoon, behlnd the
windward reef a short distance. The seven producing oil wells on the platform
are the base of the local Pemex o ration.
The island has been shaped r y prevailing winds from the southeast and
shows internal structure suggesting gradual accretion to the southwest and
northwest. Accretionary topography is particularly well developed in the
vicinity of the Welch Lodge at the southwestern margin of the island. A bordering
dune belt is also developed in this part of the island. The western
shoreline presently has the appearance of an eroding coast, but one might
anticipate development into an accreting shore wlthin the next few years since
the ship channel and spoil pile protect the island from additional destruction by
the strong northwestern winter storms. There is some suggestion that the area
between the island and the spoil piles southwest of the dock facilities 1s now
filling with fine sediment swept in from north and south. A more nearly
complete discussion of island development will be presented in a subsequent
Submarine Topography
The reef around Isla de b s is a weakly crescentic or flame-shaped structure
situated upon a gently eastward dipping platform off the main coast of
Mexico. The reef rises from a gently sloplng surface, approxlmately 120 feet
deep, to a relatively uniform flat-topped lagoon, now virtually at low-tide level.
At low-tide level, the reef is approximately eight thousand feet long in a
northerly direction from the broad, rounded, southern margin to the sharply
pointed northern tip. It has a maximum width of approximately three thousand
five hundred feet, one-third distance from the south. From the area of maximum
w~dth, it thlns northward by both leeward and windward reefs converging with

ISLA DE LOBOS REEF, MEXICO 11
a gently eastward-arched pattern. The southern margin is much more rounded,
but with an abrupt southwestern termination (Plate 1; Plate 3, fig. 3).
Low-tide outline of the reef is a rough approximation of the shape of the
maln reef mass. The reef, as now delimited (Plate I), extends to a depth of
70 or 80 feet, and at this depth is slightly over twelve thousand feet long from
south to north, and is approximately six thousand feet wide normal to this, at
the southern end of the island, although the outer reef boundary is somewhat
irregular (Plate 2).
Main topographic features associated with the reef complex which can be dif-
ferentiated are: a flat lagoon; a deeply grooved leeward reef; a more complexly
grooved, but somewhat more uniform windward reef; a broad fan of calcareous
sand which stretches southward from the reef and island; two broad, pointed,
tongue-like sand masses which extend westward and northwestward from the
southwestern and northern tips of the reef; and the rocky slope east and north-
east of the reef (Text-fig. 3).
A shallow, weakly saucer-shaped lagmn is reef-rimmed, with the margin
well defined as an algal ridge which reaches to low tide. The ridge is shown as
a dashed line on Text-figures 2, 5 and 6, and Plate 1, for the exact position is
difficult to map.
Maximum depth within the lagoon, except for the ship channel, is approxi-
mately 8 feet in the northern channel, an eroded depression in the lagoon floor
at the northern end of the island (Text-fig. 3, 6). The original channel is
interrupted by the ship channel and spoil heaps. Depths range up to slightly
over 5 feet east of the spoil heap and up to 8 feet immediately west of the large
spoil heap opposite the dock area. Elsewhere within the lagoon a more shallow
channel is developed between the boulder ridge and the small spit at the south-
western tip of the island (Text-figs. 3, 6), with a maximum depth of less than
4 feet.
The vast majority of the lagoon is within two feet of low tide, and much
of the area populated by the flat turtle-grass, Thalassia, is exposed at maximum
low tlde. Small irregular depressions are developed within these flats where
sediments have been removed to the rock floor of the lagoon. Thqr are rarely
interconnected, but do evidence the depth of the rocky substrate upon which
the plants Thalassia and Halimeda have perched a trapped sediment cover.
only locally is there a moat or depressed area behind the marginal rim.
In some regions of the southeastern margin, a weak moat is developed behind
the reef flat where depths may range up to 3 or 4 feet in limited areas. A
similarly weak moat is developed at the northern end of the reef, where the
Lithothamnium ridge forms a barrier near the low-tide level, but the interior
behind the ridge is depressed up to two feet. Elsewhere, as in the vicinity of
the wrecked liberty ship (Plate I), the reef flat slopes lagoonward and maxi-
mum depth of two or three feet is reached some distance away from the lagoon
margin.
Leeward Reef
Topographic expression of the leeward reef is characterized by deep,
steep-walled but broad grooves, separated by equally broad, flat-topped spurs
(Plate 1). This pattern is developed from near the entrance into the ship

12 J. K. RIGBY & W. G. McINTIE
,
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TEXT-FIGURE
3.- Main topographic regions associated with the reef complex at Isla de
Lobos. The reef itself is coarsely stippled, and flanking sand regions finely stippled.
Tongues from the western tips of the reef are thought to be sand swept from the
reef. somewhat like the horns of a barc-han dune. Calcareous sand dominates in
these tongues and in the apron of sand west and south of the reef. Terrigenous
sediments are most comlnon flooring the western detrial plain.
'. -.

ISLA DE LOBOS REEF, MEXICO 13
channel, northward along the western margin of the reef to opposite the
northern tip of the lagoon.
Grooves are relatively straight, from 30 to 50 feet deep below the summits
of bordering spurs, and vary from 100 to as much as 400 feet wide. They are
flat-bottomed and slope gently westward. All are blanketed with sand and
have steeply sloplng margins where sand has cascaded through the porous
reef to form small scale alluvial cone-like features. Most have abrupt termina-
tion at the base of the growing reef, but continue as minor grooves and spurs
up into the livlng coral mass. Most have bottom slopes of 10 to 15 feet per hun-
dred feet in their initial reefward development, but flatten abruptly so that
slopes of less than 10 feet per 500 feet are characteristic of their lower courses.
SIX major grooves or arroyo-like depressions cut into the leeward reef
(Plate 1). These are spaced six hundred to one thousand feet apart by broad,
flat-topped spurs, and are from 600 to over 1400 feet long, with longest ones
in the northern and southern parts of the reef.
Spurs of the leeward reef rise abruptly from a gently sloping sand apron
along the western margin of the mass. Tips of spur development may extend
to as deep as 75 feet, but throughout its length, the reef toe begins at approxi-
mately 70 feet deep. Spurs have a nearly vertical rise of a few feet at their
termini, and then a gently convex upward surface which rises relatively evenly
toward the reef crest at the lagoonal margin.
The leeward reef is widest off the northern and southern tips of the lagoon
where it is as much as 1200 to 1400 feet from the reef toe to the lagoon mar-
gin. It is narrowest opposite the northern end of the island where it is only 400
feet from the toe of one of the spurs to the reef crest.
W/indwavd Reef
The windward reef is developed along the arcuate southeastern to north-
eastern face of the topographic prom'inence (Plate 1) and is typified by
numerous radiating, V-shaped grooves separated by sharp-crested spurs (Text-
fig. 4). Broad, open, flat-bottomed grooves such as characterize the leeward
reef are wanting. Rough channeled ground shows up from the southeast mar-
gin of the reef to opposite the well platform, but to the north of that platform
for approximately 1500 feet, profiles are relatively smooth. Ulanneled reefs
are also developed near he northern tip of the lagoon.
Narrow, but often deep, vertical-walled grooves are common in the upper
surface of the reef, but show prly on fathograms, for even in shallow water,
channels a few feet wide are necessary to make an impression on the record.
Where examined in the water, local relief within the middle part of the reef
approaches 30 to 40 feet in some areas, but in general, there is only approxi-
mately 10 feet of local relief over most of the reef surface.
Base of the reef is well differentiated at the southeastern margin of the
lagoon for it rises aibruptly from the gently sloping sand apron and then slopes
uniformly toward the reef crest. Toward the northeast, however, the base of the
reef is poorly defined on fathograms for the distinctive sand apron cannot
be d~fferentiated and sample attempts indicate that the reef is built upon a
rocky surface.
The windward reef is widest at the southeastern margin of the lagoon
where it is approximately 2000 feet from the reef toe to the crest at the lagoonal

14 J. K. RIGBY & W. G. McINTIRE
TEXT-FIGURE 4.-Fathograms of lateral traverses in the leeward and windward reefs at
Isla de Lobos. A. Fathogram of the leeward reef from near the entrance of the ship
channel northward to west of the well site platform. Deep flat-bottomed grooves
and steep-sided, but flat-crested spurs are typical. Horizontal distance not to scale.
B. Fathogram of the windward reef east and northeast of the well site platform. V-
shaped grooves and sharp-crested spurs are typical. Horizontal distance not to scale.
margin (Plate 1). It is narrowest in the vicinity of the well platform where it
is approximately 1200 feet wide. It is slightly wider at the northern end where
it is interpreted to be 1600 to 1700 feet wide opposite the northern tip of the
lagoon.
Windward reef development extends as a "horn" north of the lagoon for
nearly half a mile. The extension is not a simple ridge, but appears to be two
or more somewhat parallel ridges, one an extension of the present reef trend,
and the other parallel to, but seaward of the first approximately 1000 feet.
The latter is not as regular and appears to have several major V-shaped
grooves cut into it.

ISLA DE LOBOS REEF, MEXICO 15
Southern Sand Apron
A broad apron of coarse to medium-grained calcareous sand extends south
from the reef mass (Text-fig. 3; Plate 1). It can be subdivided into two broad
areas--one with a moderately steep slope developed at the toe of the reef, and
the other as a long low ridge which extends south of the reef for at least one
mile, the limit of our traverses.
The Inner relatively steeply sloping apron buries the toe of the reef Imdly
and seems to head In an area of relatively shallow water at the old ship channel,
south of the lighthouse, where the reef IS abruptly terminated. Here the sand
wedge rises to within 20 feet of the surface, but gently slopes southward and
southwestward at 20 to 25 feet per thousand feet (Plate 1). It has a similar
slope around the southeastern margin of the reef and shows a distinctive
change in slope from the steep reef and the more gently sloping outer sand
bank. It is easily detectable on fathograms from directly east of the island,
southwestward to oppos~te the boulder ridges, southwest of the island.
The outer, more gently sloping r~dge of sand extends from the southern tip
of the reef and marginal santd apron, southward into deeper water. It is a broad
ridge with a length of approximately one mile and an east-west relief of 10
to 20 feet, rising - from the nearly flat floor of the platform.
This accumulation of sand is interpreted as reef-derived calcareous sands
swept into the lee of the reef by strong currents generated during winter storms
from the northwest. It is also possible that the ridge is a relict feature of a
buried or thinly veneered Pleistocene topography, or even an older feature,
upon which the linearly arranged reefs of Isla de Lobos, Medio, and Blanquilla
have developed.
Northwestern and Southwestern Sand Tongues
Two well-defined ridges or tongues of sand are evident beyond the northwestern
and southwestern tips of the reef (Text-fig. 3; Plate 1). These are
considered to be sand accumulations based upon ~solated soundings and character
of the fahograms. Both accumulations are linear ridges extending leeward
from the reef mass like horns of a barchan dune and are thought to have
somewhat a parallel origin. Strong bottom currents were observed to parallel
the reef and are thought to be mainly responsi'ble for shaping these features.
The southwestern ridge extends for at least two thousand feet from the
toe of the reef and 1s at least 500 and possibly as much as 800 feet w~de. It is
approximately 30 feet high near the center of its development. It is slightly
higher near the toe of the reef where it rises as much as 35 or 40 feet above
the general base of the platform. It is interpreted as sand swept by long shore
currents from the sand apron at the base of the old ship channel south of this
island.
The northern tongue is adudly two long linear ridges extending northwesterly
from the base of the reef toward Medio Reef, a small, mainly submerged
reef northwest of Isla de Ldms (Text-fig. 1). The ridges are evident for at
least 4500 feet beyond the tip of the reef, approximately 7000 feet beyond the
tip of the lagoon (Plate 1). The southern ridge is most clearly defined and is
approximately 2500 feet wide at midlength. It rises approximately 35 feet abve
the general surface developed west of Isla de Lobos. The northern ridge is of
similar proportions, though perhaps slightly longer.

16 J. K. RIGBY & W. G. McINTIRE
These broad low ridges are interpreted, like the similar feature to the
south, as an accumulation of sand deposited by long shore drift of currents
generated by prevailing winds. Like the southern ridges, however, these too
may be relict Pleistocene features, now only thinly veneered by sand.
Western Plain
The sea floor west of Isla de Lobos is an eastward sloping, sand-veneered
plain, except within two or three thousand feet of the reef, where the sedimentary
surface slopes gently westward (Plate 1). Junction of the two surfaces
produces a long linear depression 120 feet deep, approximately one m~le west
crf the margin of Isla de Lobos lagoon (Text-fig. 3). This depression is divided
into two closed baslns 20 to 30 feet deep by the southwestern sand ridge or
tongue, developed west of the boulder ridge and the southwestern tip of the
lagoon.
The weste,rn flank d the depress~on slopes approximately 50 fed per
mile, an,d the eastern one slopes neanly five times as steeply at 50 feet per
thousand feet. The eastern slope forms a broad sand apron at the base of the
reef and is composed largely of reef-denved calcareous sed~ment, although
some terrigenous clasti,c g~ains were noted in samples. On dhe other hand, the
western slope is composed largely of land-de,rived clmtic grains. Samples contain
mainly quartz fragments wibh ,same ferromagnesium minerals, volcanic
rock f~agments, obsidian, and mnsiderable calcareous debris. Some samples
oonltained la large propodion of silt and clay-sized clastic material. Sediments
accumulating in the area are conrsidered ,qpical of drift from eitiher the R,io
Tuxpan or Rio Panuco, but in the immediate vicinity of the reefs, calcareu>us
sediment masks the less abundant, terrigenous, detrltal material.
Eastern Rocky Slope
The area beyond the reef, east and northeast of the well platform, is
mainly one of rocky exposure (Plate 1; Text-fig. 3). Several attempts to obtain
samples with a clamshell sampler failed, except for recovery of small d-
care- rack fragments.
Topgraphic expression is similar to the obviously s'and-blankeked regions
to the souluh and west d the reef, and would prdably have been included wieh
those areas were it not for the dvioudy rdy substrate evidenced by stuck
anchors and empty samplers. It is la relatively smooth area, sloping gently sea-
ward toward the northeast. Only I~ally have broad V-shaped gullies cut
upslope taward the reef.
Throughout most of the area where we have sufficient control, the region
slap at bhe rate of 50 feat per thousand feet near the base of the reed and
only 25 to 30 feet per &hown,d feet at a distance of one mile from the reef
crest. The greatest depths recorded in the immediate vicinity are those in
excess of 160 feet, the limit of our fathometer, northeast of Isla de Lobos
(Plate 1 ) .
HYDROLOGY
Circulation
Normal circulation wi'thin the lagoon and laround the reef is largely the
result of waves driven by he prevailing muhastern winds. Periodically

ISLA DE LOBOS REEF, MEXICO 17
strong winds from the nocvhwest ,interrupt bhe general pattern and may Iwal,ly
reverse bhe dominant water motion.
Norm1 cirmlation within he lagoon is the result of waves pilirng onto
the eastern margin of the reef and spilling off the western side. This results
in a gened westward dnift of water over the entire shallow surface (Text-fig.
5), )but locally currents are moderately strong. Two areas wi.th channel resbridions
fat the sc~ubhern end of the island have relatively strong currents, albhough
not of constant velocigr or dtirection. One ims developed between the
split at the southwestern tip of he island and the barrier of bouldery rubble
on the reef cr&. It is rhis current which constructs the spit and the ,loose
sh~fting ,sand bar in front of it. Rubble is .swept f,rom the lagoon to bhe east
and deposited at the mkhweutern tip of the island on the lee of the spit.
Vdlwitia of 2 to 3 knots were noted in ,the construded channel.
The other channel occurs at a break in the boulder ridges on the reef crest,
and )is known as the older ship channel. Before the dredged channel was constructed
into the northwestern tip of the island, this break in the reef was the
main entry to the island. A more consi(stent current flows through thi's break
and to the southwest. Much of hhe soubhern lagoon is drained through this gap,
carrying with it considerable sediment from the Halzmeda and Thalassia flats of
the lagoon, onto the sand apron south of the reef. Velocities of 3 to 4 knots
are not unusual in low p e s thmgh ,the break in the reef crest.
One of the strongest currents noted wi'thin the lagoon is developed at the
nosbhern end d the well site pl'atform. Wibh construction of the causeway and
ship channel from the ~sland, northeastward to the well platform, normal circulation
wi~th'in the northern 'part of the lagoon was blmked. Water which would
nomlly hsve paured around the no&hern end of the island is now deflected
as much as one thousand tfeet to )the north where it flows past the well platfotrm
and onto the western reef (Text-fig. 5). Weak channels are now being
excavated along the northeastern margin af the platfonm and will probably
continue to develop as long as normal cirmlation is blocked by the spoil pile.
What its considered #the normal, pre- hip channel, lagoonal cirmlation pattern
is now developed only north af the well platform. Wind-driven waves
pile water onto the Iapn filats neady at right angles to the reef front. This
water d'rains off ,the western margin where the reef crest is slightly lower.
Tihere is some southward deflection of water ismmediately norbhwest of the
well site platform, but most lagoonal drainage in the northern prt is diredy
westwatrd across.#he Itagoon, through the rather ill-defined Lzthothamnium red
crest.
Interruption of the nomnal, pre-ship channel, current pat.tern is well demonstrated
at the northern end of the ivland where a coral-populated channel
was excavated in the lagoonal flats. The channel is as much as 8 feet deep,
~ut into flats wibh an average deph of less than two feet, and is approximately
200 feet wide. These depressed areas were populated with large coral heads
of species most common in outer reef communities. These channels are now
sites of hegrained deposition, however, for they are abnormally deep depressions
in the lagoon flats and are fil,led with quiet wter dammed by the spoil
piles. Upper surfaces of tal'l coral headls within the channel are blanketed wi'th
fiine ~edi~ment, and only the nearly vetrtical and overhanging margins of the
heds are still alive. These abno~mal lagoonal mrnmunities are now 'king overwhelmed
by ficne calcareous detnitus.

18
J. K. RIGBY & W. G. McINTIRE
TEXT-FIGURE
5.-Approximations of current directions and velocities in and adjacent to
the lagoon at lsla de Lobos. The island and spoil heaps are shown in black, the
boulder ridges to the southwest as white stippled on black, and the now-blocked
North Channel as finely stippled. The reef is coarsely stippled. Currents generally
move westward across the lagoon, except for those deflected around the island and
spoil pile. North Channel was excavated by normal drainage around the island prior
to dredging of the ship channel, but both parts are now filling with sediment.

ISW DE LOBOS REEF, MEXICO 19
Outside the lagoon, circulatwn around the reef is mainly from a t or
souoheast toward the west (Text-fig. 5). Currents af 4 or 5 knots were o&
served at ti,mes along the southern margin af the reef and were noticeable to
a depth of over 50 feet. At times, even at the bare of the reef in water 65 to 75
feet [deep, the curreat was strong and moving in a southwesterly direion. No
deep diving was done at the northern end of the reef, but surficial drift is
rapid and suggests a moderately strong current at d+ as well.
A )moderate current was noted by Rector and Adams in deep dives into the
sandy and ,muddy 'area west of the reef. In 120 feet of water hey noted a
derately northwesterly dfiA at the Ilrattm.
Major *sudace dlr,ift was from the no&hwest for approximately one week
during the middle of August. Fresh-water hyacinths and other debris froan the
flooding Rio Panuco moved p t the island as a con,tinuous stream. Jirge dts
of flotant and individual logs were also drifted southeastward, along with mnsiderable
fine sediment which prduced murky water for over one week.
M a s whi& were normally clan were li'ttered with fragments af root
systems of many fresh-water, aqueous plants. At the same time, the prevailing
winds were weak and major winds were from the northwest, presumably
blowing ,the surface water before them. This one-week storm may be a summer
equivalent to the cold northern storms of the winter, termed nortes, which
reverse the normal circulation patterns.
No&es have a pronounced effeot on sedimentation and topography as well
a do the prevailing wids. Perbps one of the most noticeable effects would be
rhe loss of the small spit at the southwestern tip of the island. It was reported to
have been destroyed, dter ,being breached, in a single storm. Much of this
sand must have been washed to the south through the old shrp channel onto the
fl,mkijng sand apron at the base of ,the reef. The reversal of circulation produced
by the storms prchbly has been ,the nuin erosion force along the northwestern
shore af the islland, in tabout the same manner as destruction of the spit. These
areas of he island are adjusted bo the normal airculation produced by the prevailing
winds and are unstable to winds and currents from the north or northwe&.
Turbidity
Water bathing the reef and lagoon of Isk de Ldxs is usually ~uff~iciently
clear hat objects can be r~ognized in up to 20 feet of water on the windward
side of the reef. Leeward, and within #ohe lagoon, 6ine sediment 'is often
in suspension and increases the turbdi.ty. Most turbid waters are those within
the ,ship channel where fine Iagmnd sediments, mixed with residual drilling
mud, are constantly churned into suspension by movement of boats and barges.
D,i8stphut8ion d turbidity may 'be a factor in differentiating windward and leeward
reef communities, for with rare exceptions, windwad water is slightly
less .turbid ,than leeward water, some of which has spilled across the sed,imentladen
lagoon from the windward edge. In most regions, however, water is
sufficiently clear that photographs can be taken to the toe of the reef; although
at depths below approximately 25 feet, it is impossible to do so without a tripod
or auxiliary lighting.
Unmwl turbidity resulted from flood waters af the Rio Panuco which were
blown southward along the coast during an atypical period when winds from
the northwest were dominant. ?These 'hrrbid waters reduced visibility to only a

20 J. K. RIGBY & W. G. McINTIRE
few feet and mad'e photography of all but the shallowest features nearly im-
possible wlhhout some artificial light.
Clearest water resulted frm a return to prevailing winds, coupled with
extremely low tides. Even water 'within the ].agoon and on bhe leeward edge of
the reef was clearer than the normal gulf water had been during much of
our period of investigation. Such clarity is probably related to reduced turbu-
lence within the lagoon and decreased water flow through the lagoon and reefs.
Tides
Hourly observations on tide level were made during the two-day period of
August 6 and 7 at the Pemex docks on Isla de Lobos; and in addition, scattered
crbservations were made at a still-water gauge set up south of the island. Tidal
range at the dock durlng the observed period was 1.8 feet, and this is assumed
to be an average Lower tides were observed during the latter part of August,
however, when maximum low tides showed a variation of 2.7 to 2.8 feet.
During average mid-cycle tides, all but the highest promontories within the
lagoon remained below water. At maxlmum low tides, however, 15 to 20
percent of the lagoonal floor was exposed and circulat~on across the reef complex
was nil.
There IS but a single tidal cycle per day, w~th the cycle advancing at the
rate of approximately 1 hour per day, as is typical elsewhere. Flooding tides
rise rapidly and remain at crest for as long as 6 hours before the relatively
slow ebbing takes place, followed by a low still stand of 2 to 3 hours.
Tidal fluctuation, athough relatively small, controls the upward growth of
Thalassia. At maximum low water these plants are killed by exposure, wlth the
end result of patchy development within the lagoon. Similarly, vertical reef
growth 1s limm~ted to below the maximum low water stages.
HABITATS AND COMMUNITIES
Many earlier workers on marine ecology have recognized the marked developmenlt
of associations af benbhonic organ'isms, often with mutual exclusion
or at other times with forms of broad distribution. On Isla de Lobos several
dfisbinct hjabitats and communities can be differentiated wilhin the reef complex
(Text-fig. 6; Plate 2). Habitat in this sense is used as the combination
of blcvloglcel and physical faators of the environmen,t of either the organism
or of the community. A cornmunilty is wns~dmered as a distinct group of organisms
living together, much as used by Newell et a1 (1959) in their study of
the Aadros Pladorm In the Bahama Islands.
Using the above definition, a variety of methods of differentiation of
habitats is passi~ble. They may ,be wbdivlded on the basis of salinity, depth,
temperaimre, turbulence, light, type of substrate, or ~nnumerable other prameters.
Far the present study we have found it suitable to subdivide habitats
into three broad categories: lagoon, reef, and surrounding sed~iment apron,
with sullldiviuions In each, based in large part u n character of the substrate.
Thorson (1957), Newell et a1 (1959), an many other workers in marine
ecology have shown thlat marked differences exist babeen communities estab-
licshed on various substrates, although such diiferentiation is not always defini-
tive. In a reconnaissance study such as ours, however, it is often the most easily
documented and mapped differentiation; for in these limited observations, sedl-
r

ISLA DE LOBOS REEF. MEXICO 2 1
TEXT-FIGURE
6.-Substrates associated with the reef at IsIa de Lobos. 1. reef and rocky
substrate; 2. pebble substrate composed largely of algal oncolites; 3. sand substrate
composed of relatively large fragments of corals and Hulzmrdu plates; 4. rocky sub
strates within the lagoon swept clean by normal drainage (except where the North
Channel has been blocked by the construction of the ship channel); 5. unstable sand
substrate and barren semi-stable sand; 6. boulder ridges.

22 J. K. RIGBY & W. G McINTIRE
ment character and asmiation of organism can be quickly &served. Habitats
remgnized on Isla de L b reef are: a rocky shore, a sdy shore, unstable
sand, stable sand, ,and idratidal rocky bobtoms within the lagoon; gravel kttoms,
and rocky 'bottoms within ithe reef; and a stable and unstable sandy
bottom in the surrounding deeper water.
In &his sense we differentiated habiitat comunities, as used by Newell et af,
(1959, p. 197-198), rabher than organivm communities or biacwnoses (Miobius,
1877). Organism cornmunitties are those defined on the basis of the organisms
themselves, with l'ittle or no regard to physical or chemical factors of the habitat.
Differentiation of biocoenoses is virtually impossible in a reconnaissance
study, since mutual biologic relationshi~p of animals and plants could not be
demonstrated. Some such relabionships are hrvable, however, and were mnsidered
although the ultimate causal relationships were not investigated.
Communit~es differen'biated within the lagoon include: a balanid barnacle
rocky-shore community; a poorly developed, unstable sand community; a group
af communit,ies charaoterized by Paditza, Caulerpa, and Penicilfus developed
on a scoured, rocky, infratidal habitat; an Arenicofa (?) community, a Thalassza-
Halirneda community, a Thalassia-Porites community, a Thafassza-Diploria
strzgosa connnunllty, and a Lithothamnzum pebble community. An unusual coral
community dominated by Montastrea annularrs 1s developed within a mured
channel at the north end d the ~vland, deep within the lagoon, and is considered
~sepamtely, although ~t has much in common with the leeward reef.
Di\fferemtiated reef communities are: a Drpforza cfzvo~a community as the
inner pavement of the reef flat; a LMotharnniunz ridge at the reef crest; an
Acropora palmata community immediately in front of the crest on both leeward
and windward reds; a Montastrea ann~laris communi,ty in moderately deep
water on the leeward reef; and a parallel Diploria strzgosa community in the
windw,amd reef. A Montartrea cavetnosa community is developed at the base of
batrh leeward ad windward reefs, and is iflanked by the loose sand of the
surrounding platform apron.
- -
Sufficien!t observations were not made of the surrounding deeper water
habitats, hence community differentiation is not attempted from our isolated
dredge lhauls and scattered observations on deep d,ives. Ijt is apparent, hawever,
that differing conditions are present windward and leeward, and differentiation
would be impossible.
THE ROCKY SHOKE
ROCKY-SHORE HABITAT
A rwky-shore habitat is only locally developed on the reef and island of
Isk de Lob, partially on man-made very recent structures, and partially on
nabural accumulations of coral heads on the crest of the reef, swth of 'the
island (Plate 3, figs. 3, 5). The hter area forms the oldest rocky exposures
and ,the area where shore wnation is mast well developed. Elsewhere, a rocky-
shore harbi,tat is formed by coarse debris in spoil piles along the ship channel
(Plate 3, fig. 2) and 'by the concrete well platform and flank~ng protective
ddbris.
Boulder ridger.-Two long, linear ridges of t d coral heads were developd
along the southern margin of the reef (Plate 1; Plate 3, figs. 1, 3, 5) during
the 1951 hurricane, a storm which nearly destroyed the small1 sand island

ISLA DE LOBOS REEF, MEXICO 23
wikhin tfhe lagoon. Boulders and blocks of the ridge are composed of h d of
Diploria and Montastrea up to 4 or 5 feet in diameter, derived from the lower
pa^ of the reef fronsting on the deeper sand apron. These heads were tossad
onto the crest of the Lithothamnium ,fidge into shallow water.
The 1,arger of the two ridges is approximately 1500 feet long and up to
150 feet wide (Plate 3, fig. 3). It is relatively low so that waves break thm&
and over mwt of the structure a't high tide. A small sand cay is developed
at the widest and highest western part, but the remainder is of bauldery ruble
(Flake 3, fig. 5).
The smaller d ,he two is east of the old (boat channel (Text-fig. 5; Plate 1 )
and is less continuous and much lower. It is only approximately 500 feet long
as a cont~in.uous mass of blocks, but continues on eastwwd another 500 feet
as isolated tossed heads on the crest of the reef. It is only 50 or 60 feet wide
at the widest and is mainly buried at high tide. Even at low tide, however, waves
commonly break over wen the highest boulders.
Base of both bouldery masses is sharp on the seaward edge where bl&
rest on Lithothamnium pavement, but on the protected lapnward side, sand
is now blanketing the lower edge (Plate 6, fig. 5).
Spozl piles atzd well p1Ftforrn.-Recent man-made stmctures provide another
area where the rocky-shore habitat is developed. Coarse spoil, particularly
where washed near the high-tide line, and debris surrounding the concrete
wel,l platform could function as a habitat where the rocky shore community
might b m e established.
ROCKY-SHORE COMMUNITIES
The ~b~lder ridges, spoil haps, and the well si,te plabform are the only
places on the island where rocky-shore communities could become established.
Such carrununities are 'poorly developed, probably because the habitats have only
recently apened.
Within the tidal zone and supratidal zone, only small clusters of balanoid
barnacles have become established. None of the d,istinctive intertidal or low
supratidol molluscan faunas common in he Bhma Islands and elsewhere in
the Carri'bbean area were observed. The didindive colo&on of the lower
part of a rocky mat is developed, however, for boring algae have imparted the
diagnostic yellow-gray color to lower parts of exposed blocks and the dark,
so~mber gray-brown to upper parts. These color zones probably correspond to
si,milarly mlorpd belb developed in the Bahm Islands (Newell et d, 1951, p.
17-19; Newell et al, 1959, p. 206-208); but the distinctive fauna, except for
barnacles, is not developed. One of ,the hopes for a continuing study of the
Isla de Lobos region is that of watrhlng a new habitat being ppulated
Baal 'parts of the boulder ridges, below low tide, are now cded with
wbby-lwking patches of pnk rand purple Lithothmnnjum and with brown
fiIamentous algae. In a few favorably expad spots small heads of purple
Siderastrea radians have developed up to 4 inches in diameter. These corals
ore most common near the break in the reef at the old ship charnel.
Padina and some orher bmn dgae are common on boulders at the exped
emds af the boulder ridges where cuments are strong. They are often intergrown
with a mat of f;ilamentous algae and d l daarerrus algal crusts, but
do not extend far onto the lagmnward protected side d the ridges where
currents lare weak and sediments are accumulating.

24 J. K. RIGBY & W. G. McINTIRE
Numerous small gastropod6 are common on many of the 'boulders on ,the
back af the boulder ridge. They are often asmiated with sm,all hermit crabs
and appear to be grazing on t'he fi1,arnentous algae.
THE SANDY SHORE
SANDY-SHORE HABITAT AND COMMUNITY
Isla de Lobos is completely surrounded by a relatively narrow, steeply slop-
ing sandy beach, but little attention was given the hhitat since the only readily
apparent animal inhabitants are abundant, small burrowing crabs. Characteristic
plant zonation is developed, however, along the eastern and southeastern
margin of the island and will be discussed in a subsequent paper dealing with
island development and history.
THE LAGOON
INFRATIDAL ROCK-BOTTOM HABITATS
Exposed, eroded, rocky surfaces are well developed in the lagoon at the
southern margin of vhe (island, in the region of scour east of khe sand acmulation
and sipit south of the Welch Lodge (Plate 1; Text-fig. 6). Simi,lar surf#-
are now developing east of the well platform in channels related to shift
in water flow from the windward to lmrd margin of the lagoon as a rebult
of construotion of the hip ch'annel.
The barren area at bhe southern margin of the island is limited by the
wedge of moving sand on the west and patches of Thalassra on the east (Textfig.
6; Plate 3, f~g. 1). It begins &mpIy dfshore at the beach ,&ep and
extends southward to the crest of the reef. h e
heads of coral li,tter the
bottom arud are covered with la vaniety of algae. Although boundaries are some-
what irregular, banren rocky substrate covers an area approximately 200 feet
across, both normal and paralllel to the southern shore of the island.
INFRATIDAL ROCK-BOTTOM COMMUNITIES
Several distinct communities can be recognized wi,thin these smaIl areas, but
are undiltferentiated on the mp (Phe 2) because of scale. Most diskindive
organisms are algae which can at,tach to tohe current-swept bottom. Prtdina, an
ear-like brown alga, is common in regions of barren rocks. Cdulerpa, a clustered
grape-like green alga, and Penicillus, a brush-like calcareaus green alga, are
distinctive of other communities where bhin veneers or patches of sand are
available for population. These communities grade into one another as the
substfiate character gradually changes.
Padina sanctaecrucis, the distinctive plant of i(ts colmmunity, is locally com-
mon where currents ,are most vigorous and sand has been &wept away so that
r& protn.de (Plate 4, fig. 6). These algae farm in ear-like masses up to 3
or 4 inches high and are closely packed on m5t rocky surfaces. These plants
make the bottom seem brownish gray when seen underwater The Padina com-
munity is well developed around the brase of the eupd part d the boulder
ridges and on most barren rocky surfaces 2 few inches high, above the zone
of maxllmm sand transport. The camimunity is also thriving on the newly
drdged !blwks in the middle of the north side of the well platform, and is
lwally common in areas east of ,bhe platform on most of the loosened blocks

ISLA DE LOBOS REEF, MEXICO 2 5
and tossed coral heads. It has yet to repopulate the current-swept northeast cor-
ner or the nonthwestern corner or western side of the we181 slte block, for in
these areas only fine, hair-like, filamentous algae have become established.
Caulerpa cupressozdes and C. sertularzordes longrseta are common in the
barren region and are bhe distinchive pbnts of their community (Plate 4, fig.
4). These algae grow In stolon-lsike fashion after becoming established in small
sandy patches in the generally bamen rocky region. Long strings of the algae
now trail with the current where loosened from the substrate, or form
a close network of ~nterlacing stolons in a thin sand cover, where fixed. Eases
of the colonles are commonly exposed, far the thin sand veneer is constantly
in motion and only locally are their roots suff~clently dense to hold the granular
substrate.
Two species, C. ct4pressordes and C. .rertularzoides, occur In sandy areas in
the rocky zone. The larger, more bushy C. cupressozdes is domlnant and most
widespread in the sandy zones, and the smaller, b~foliate form wlth two series
of branchlets, C. sertularioides, occurs in the less deeply sand-veneered areas.
Both seem able to survive in the same depth water and in waters of equal agitation.
Thelr major llmiting factor seems to be variation in depth of sand on the
substrate.
Penicillus sp. is the indicator plant of an additional algal community in
which the rocky substrate 1s only thinly veneered wi'th sand (Plate 4, fig. 3).
These brush-l~ke forms are common around the western margin of the island,
and in the m,ore sandy regions of the rocky area south of the island. These algae
have numerous, small, ha~r-like roots which stabilize sands and provide areas
where they cannot only maintain themselves once esbablihed, but can form a
favorable area for repopulation and for establishment of other organi,sms.
UNSTABLE SAND HABITAT
Loose drifting sand is accumulatrng within the lagoon only at the beach
margin and at the southwestern tip of the island (Text-fig. 6; Plate 3, fig. 1).
Sand-size shdl debris is accumula~ing in a rippled and shifting bar off the
southwestern tip of the is1,snd. It is expressed at the surface as a small sand
spit slightly over 100 feet long and rising up to 3 or 4 feet above high tide.
In the lagoon it is a blanket of shiftlng sand extending southward as a triangular
area 200 feet aaross. The sand is a~cumula~ing in an area of moderate
current between the spi8t and tihe eastern edge of a hurricane-tossed boulder ridge
on top of the reef crest. It is burying a relatively smooth rock floor and is KS
much as 3 feet deep at its northwestern end near the beach. Where thicket it
has developed a steep leeward slip slope, but thins gently eastward to a
feather edge of rippled sand over a current-swept rocky surface. The bar is
composed mainly of coarse-grained sand to granule-s~za pantlcles, worn mainly
from corals and algae common in the lagoon. Much of the detrital material is
readily identifiable as Halimeda fragments, altihough Porrles fragments also
play an imporbant role.
Upper surface of the sand wedge is in constant motion, for with both
flmd~ng and ebbing tides, moderateily strong currents flow through the restriction.
Dominant movement 1s from east to west and the surfxe is shaped
w~bh ripples ranging up t~ 4 or 5 inches high an'd up to 1 foot from crest to
crest (Pllate 4, fig. 2).

26 J. K. RIGBY & W. G. McINTIRE
UNSTABLE SAND COMMUNITY
N.o macro-organisms were found living in or upon the sand. The mass is
apparently too unstable to be populated. In addition to its shifting character,
much of the bar is exposed at maximum low tides, m&ling it a less than idd
substrate for benthonic organisms.
STABLE SAND HABITATS
Stabi,lized sand habibitabs occur Chraughaut the lagoon on Isla de L h , and
to some extent in the surrounding deeper water of the platform as well. Several
facies can be differentiated within the lagoon, all oornposed 1,argely of shell
sand or fragments of the calcareous alga Halrmeda. Relat,ively fine-textured
sands, blanketed by a leathery algal crust, occur in quiet water immediately
north and west of the island. Coatrser grained sands occur through most of the
remainder of the lapn where several different communities have been differentiated.
These coarser sands are l~argely fragments of Halimeda and fofim
the substrate into which the flat-bladed grass, l'halarsia, has rooted and in
which various sponges, corals, anemones and echinoderms also grow.
STABLE SAND COMMUNITIES
Arenicola( ?) Community
Two areas of burrowed, mounded sand are present adjacent to the island
(Plate 2). One of these is well defined In the leeward region, north of the
small splt at the southwestern tip of the island; the other is adjacent to the
nonthern end of the island, east of the camay. Both are in relatively shallow
and sheltered areas where coarse to medium-grained sand is now accumulating
and where organic refuse collects. These are probably newly developed facies,
particularly the one to the north, for prior to construction of the causeway,
relatively vigorous ,cumeltts swept the area. Development of the quiet envircmrnent
followed causeway constructwn. Both nor8thern and southern areas are
floored with filamentous algae covering a stable sand flat.
The Arenicola (?) mounds are from 4 to 6 inches high and form low
cones on the moderately moth surface of the sand (Plate 4, fig. 1). They we
most concentrated near the low-tlde line, where they are spaced up to 20
mounds per square meter in the southern development. Mound spaclng 1s progressively
less dense away from the shore, until 100 feet off shore :they are
spaced only 1 or 2 per square meter. The area is almost ster~le-look~ng, with
only the mounds and a crust of mossy, gray-bromrn filanientous algae. These
mounded sandy areas grade seaward into Perzccillus-Thala~rra blanketed sands.
In the transition areas mounds are often 10 to 12 inches htigh, but are usually
widely spaced.
The flat-bladed turtle grass, Thalassia testudinuiunz, blankets much of the
interior of the shallow lawn and occurs as scattered plants even into the
Lzthothamnrum ridge laround the margin. In the interior of the I~gocm, how-
ever, it forms dense growths which act as efficient sediment traps and forms
a distinctive facies, particularly when combined with areas where Thalarsia and
the calcareous alga Halimeda occur together (Plate 2). Halrmeda occurs be-
tween the grass plants, and forms a porous substrate through which the stolan-

Sealevel
30'
A
Porites Community
Thallasia Community
-r
0 200 feet
Lithothamnium Pebble Community Lithothamnium Ridge
Seolevel -
2 0'
Acropora polmata
Community
c I Thallasia Community
Thallasia Community
! 0' Lithothamnium Pebble Communityf
? ZOO f eet Diplorio clivosa Community
Spoil Pile
20, Lithothamnium Ridge Community
C
TEXT-FIGURE
7.-Topographic and community profiles within the lagoon. A. Profile
along Traverse 5, from the windward edge, across the lagoon, to near the leeward
edge, north of the well platform. B. Profile along traverse 6, from the leeward mar-
gin of the lagoon, east to the spoil pile opposlte the docks. C. Profile along traverse
7, southeast from the island across the lagoon to the windward reef. Vertical exag-
geration x 10.
Sealevel

28 J. K. RIGBY & W. G. McINTIRE
like roots of Tbala~sia can easily penetrate. The two plants together form a
porous, spongy-textured, sand-covered lbottom.
Clum,ps of Thalmsza rise above the general surfwe of rhe rocky substrate
hke clumps of brush which have b~apped sand In western deserts (Plate 5, f~gs.
1, 2). In some instances, clumps of grass and Halimeda r18se as much as two
feet above surrounding areas. This is particularly true at the western edge of
the Tbalassia banks south of the lsl'and, where the margins of the grassy clumps
are 'being eroded, and have almost vefillcd sides, protected by the complex root
' system of rhe gross. Some of the &rate mus,t hlave been eroded, for segments
of roots trail down current some inches or feet from the clumps. In most of the
region, the grass flats hlave grown to trhe level of maximum iow water, so that
during this low-water stage (Plate 3, figs. 4, 6), the crests of many of the
clumps are bare and the grass on them is killed. Once this happens the interlor
of the clump is then eded until it can be statnlized by lateral growth of Che
gsas agaln. This produces a patchy pattern in many areas and has been dif-
ferentiated rn areas where sandy bottoms dom~nate over grassy bottoms. This
1s particularly well shown in the murhern end of the lagoon, south and south-
east of the iiland.
Small mounds of grass are composed of loose sediment trapped by babh
Halrmeda and Tbalassia. Halimeda pl~ates form much of the loose sediment
and most apparently accumulate in place, trapped beneath the protective cover
of the grming plant,s. The spongy of loose plates may reach as much
as 8 inches thick, through which and Into which the living Halzmedu and the
growing Tbala~sla mot. Fine sedlment is trapped w~thin the cover, but makes a
small fraction of the total when compared to the larger calcareous fragments of
Halimeda.
Even in the dense grass flats, however, small, Isolated, rocky-floored or
sanjdy-floored depressmn's exist (Plate 5, fig. 2, 3). These are generally mu- lated with various large anemones, sponges, small anemones, gastropoda, and
actapi. These rocky areas form small open depressions in the general gras'sy
flat, 1 to 2 feet deeper 'than the flat itselsf.
Thirs pa~rticul~ar community 1s well adapted to the shallow water environmen,t
of most of the shallow ],agoon, and is particularly wdl developed immedifately
much and east af the ~slland (Plate 3, fig. 4, 6), as well as in the interior
of the lagoon east and west of the ship ahannel north of the island. It 1s the
mod extensive community wllthin the lagoon and apparently represents the
climax cornmun~ty of the lagoon.
Thullusiu-Porrtes Community
A community of intermixed Tbalassia and Por~tes is developed along the
western margin of the Ilagmn, from west of the island, northward to w~vhin
2000 feet of he northern tip of ,bhe 'reef. West of the well platform, community
development is from 500 to 600 feet wide, normal to the reef front, but to the
south and nor;th, Porites development i,s less extensive.
Toward the west, gravels of Porites porrtes pave the lagoon floor and
gmss is less dense. In these areas living Porites 1s most common and forms
thickets up to 6 to 8 inches dmp. In local a1rea.s living Por~tes covers over half
the lagoon floor. Ait rhe inner Ilrlm~t of its development Porites porites forms
sm'all heads inttergrcrwn with Halimeda as an undergrowth to the taller Tbalarsia

ISLA DE LOBOS REEF, MEXICO 29
Oher organi.sms m mon in the community include a moderate variety of
sponges, same echi,noid)s, and isolated heads of Diploria clzvosa and Siderartrea
siderea, both of which are usually loose.
This corwnuni.ty grades lagmnmrd by loss of Porites into the sandy thick
growths of Thalassra and Halimeda; reefwiard, howwer, Porites plays only a
minor role, where Diploria clzvosa becomes dominant and scattered in with
Thalassia.
Thalassia-Diploria Community
Although isolated heads of Diploria occur through most of the lagoon, they
become sufficiently abundant along the margin of the flats that the association
is separately mapped. Corals are fairly common along !the eastern margin od
the lagoon for up to 500 or 600 feet behind the reef crest, and this zone of
abundance is included here in the Thalassia-Diplorla community, excluding
that part of the zone where algal oncolites are the dominant substrate. The
assaclation is penhaps best develaped along the western margin of the lagoon
where algal pebbles are prly developed and where a Lithothamnzum ridge is
111 defined, if present at all. In b th these areas, corals consist of isolated heads
of Diplorza clivosa, in the main, but also Sideraslrea siderea, Montastrea annu-
larzs, and Porztes bmnneri. Throughout most of the area corals comprise only
20 to 25 percent of the area, and of thi,s, Diploria clivosa would account for
15 to 20 percentt. Thalassra is present, but is not as densely spaced as in the
more sandy interior of she lagoon.
Lithothamnrum GRAVEL HABITAT AND COMMUNITY
Oncolites of Lithothamnium are developed in the lee of the windward reef,
ak the m~argin of the 1,apn and the Diplorza cliwosa pavement (Plate 2; Plate 5,
6ig. 4). The community is typically dweloped over a wide area at the northern
tilp of the reef, and fat most places abng the eastern margln of the lagoon,
southward to just southeast of the island.
Southeast of the ~sland, pebbles formed by encrusting Lithothamnium
form a band approximately 150 feet wide behind the Drploria pavement.
Lagoonward, typical sandy flats replace the pebbly base where Thalassra is
present in dense growtth,s.
In the vicinity of the wreck, east of the northern part of the island (Plate
2), similar pebbles form the surbstrate for sparse Thalassia for approximaterly
200 feet behind the coral pavemen't of the reef before grad~ng into s'and. In
the immediate vicini,ty 'of the wreck, pebbles and small cobbles are well developed
up to 2 feet deep.
Pebbles are formed by irregular crusts of algae coating mainly fragments of
Porrtes (Plsate 5, fig. 3) or mallusks, although in some pebbles there is no
obvious foreign - organlc cure.
In addition to the gravels of oncolites, Thalassia and Halzmeda occur as
wsttered planmts or colonies. Isolated heads of most of the reef flat corals cxcur
throughout the pebbly zone, but most common heads are of D. clrvosa, along
wih moderately abundant Porites in local areas. Porite.r is particularly common
In the northeastern part of the Itagoon. -
Broadest development of the oncol~b~c Lrthothamnium community is near
the northern ,tip of the reef where pebbles blanket the interior of the lapn

30
J. K. RIGBY & W. G. McINTIRE
over a wide area. In this region there is little grass and the pebbles are appar-
enbly constantly moved. This is also the reglon d best coral development within
the dominanbly pabble-f'loored facies, for here the Wer is sl~ghtly dee and
waves are more vigorous. Hds of Diploria strrgosa, D. ilivosa, Slgatrea
srderea, Porites branneri, P. porztes, and even Acropora palmata occur sc;r&ered
bhrougbut the pebble zone, but tatal probably less than 10 percent of the arm.
It is this regton which most closely paral'lels the lagoonal pattern over much of
Blanquilla Reef, presumably hause ~n both areas strong waves can sweep
aoross the flats.
THE REEF
REEF HABITATS
The reef habiiat is develaped around the margin of the lagoon at Isla de
Lobos and its distritbutlon has been dissussed eartier in the section on topography.
The habitat, as a major subdivision, extends from the low-tide line down
to at least 75 or 80 feet, b the border of the rocky bottom with the surrounding
sand apron. Within this major halvi,tat, one can recognize many microhabitats,
but three subd,ivisions with1:n the reef can be easlly differentiated.
One of phese is typical of shallow water throughout the reef and i's characterized
by vigorous currents and maximum ligh,t penetration, where algae have cemented
the structure into a solid mass. An intemediste hab~tat can be separated on the
kls of both reduced light and vigor of currents, in a region where pockets
of sand st111 persist and where algal crusts form less of the rocky substrate. A
lower habitat can be di~fferentiatd from those above by noting increase in sand
areas within the reef and almost lack of algal crusts on the broad, open, cavernous
sucface. The lower hbitat is ch,aractenized by markedly reduced intensity of
light and currentt vel~c~ty. Ekch of these three broadly di,fferen,tiable habib&
is populated by a moderately distinctive community, and certainly within each,
many more narrowly defined cwmmun~ities could be separated on a micro scale.
Vaniatlons ln exposure to surf, light, and sediments, to name just three parameters
of the environment, produce marked variation in the micro-community
within each broad zone.
REEF COMMUNITIES
Djplor-la clitlora Community
A broad zone of ahndmt Drplorta, here considered a distinctive com-
munity, is developed at the Iitgmnal margin of the reef (Plate 1; Plate 3,
figs. 1, 2) behind the Lithothamnrum ridge, where it is well defined, or at the
reef crest where the ridge is nlot developed. This pavement forms in shallow
water, just below maximum law tide, and vanies from 100 to over 300 feet
wide around the margin of the lagoon. It is also localjly develaped in front of
the Lithothamnium ridge on the leeward reef in the northern part d the reef.
The communi~ty IS vey well developed in lbhe leeward reef, opposi,te the
nonthern end of the islland. Here the reef flat consists of an extensive develop
ment of knobby, encrusting, plate-like masses of Diptora clivosa (Plate 3, figs.
1, 2). The coral functions as a 'binder on the top of the reef and extends as
isolated heads well into the lagoon and locally down into the upper part of
the seaward reef. In many areas along the western margin of the lagmn
Diploria cliz~osa covers as much as 70 to 80 percent of the area, in heads up to
5 or 6 feet in diameter and on,ly a few inches high. Pockets of and, in which

ISLA DE LOBOS KEEP, MEXICO 31
(IC~UPOTO poirnata
Community
TFXI-IIGL~R' 8 - 1'0pogr~tph1c and community profile5 ot windwart1 anti leeward reefs
and the tldnk~ng sand apron at Isla cle Lob05 Large ptoftles ha~e \ 10 vertical ewaggeration,
but smaller black profiles are without exaggerat~on A Leeward reef profiler,
oppos~te the well platforin, ne,lr It~cality 41 R Wtndwnrcl teet profilt~ southeaqt
of the island near lotaltty 38 C Mttdif~ed windward reef prc,filts \out11 nt the
islanil, trppostte the sand wedge ,~ncl \ptr uett of the old \hip channel

32 J. K. RIGBY & W. G McINTlKE
Halimeda, Penrcillus, ,and Caulerpa grww, make up most of the remainder,
alhugh Imally some heads of Montasirea an~zularrs, Szderastrea siderea, D.
strigosa, Porites porites and P furcata (?) occur scattered in low areas in bhe
Davemen,t.
1
The Diplorra clzuosa community is also developed on the lagcmnward mar-
gin of the windward reef (Plate 5, figs. 5, 6) throughout its length in water
jjust below maximum low tides. In front of the wrecked ship the pavement is
as much as 150 feet wide.
Southeast of the isliand the Diplovra clzvosa pavement is as much as 200
fed wide and with slightly more local relief bhan to the n01rt:h or in the leeward
reef. It is composed mainly of flat plates of D. clivosa, only a few inches high,
which appr to encrust like frmting. Other corials are present as small heads
throughout, but are most wel'l developed in lightly sheltered weas. Siderartrea
siderea, Porites porites, PorrtpJ furcatrt(?), and some D. strzgosa are presentt
at mast localibies, although most heads are at least partially overgrown around
their base with Litbothamnium. Numerous holes in coral heads and along their
mangins are occupied by red and purple Echrnometra lacunter and by the slate
pencil urchin. All of bhese are c omnly encrusted with algae or foraminifera.
The Diploria clruosa community is prly developed along the southern
mrgln of the reef an,d is not present at the reef crest between the boulder
ridges on eibher margin of the old ship chiannd at the southern end of fhe
. .
~sliand.
Lithothamntum Ridge Commun~ty
A low ridge, formed or crusted wi.th Lzthotharn?~zum, is developed at the
reef crest surrounding the shallow l'agoon (Plate 3, fig. 2; Plate 1). It is best
developed abng the windward edge and leeward edge of the 1)agoon in the
northern part of the reef. It is moderately devdoped along the arcuate eastern
margin of ehe lagoon from near bhe wreck, southward, to the old ship channel
and !the ridges of rock south of the ilsland. It is only poorly developed along the
leewasd edge of the lagmn, from south of the en,trance to the ship channel
ruofihward to west of the well phtform.
In the northern regions it rises as a disttinctive barrier, as much as 3 feet
above an ill-defined moat at the margin of the lagoon, and is constantly awash
wish strong surf and swmh, except when locally exposed during maximum low
ti,des. En bhis ,area it 1s 70 to 100 feet wide, w,ith a transition into coral-encrusted
regions bo~h haponward and seaward. In this reg~on if hias a typical pink to
light gray or purple, massive, but gnxsly cavernous, surface, with most open-
~ngs occupied by slate pencil urchins or red and brownish purple echinoids.
Locally Dlplorza clruosa forms heads as much as 3 to 5 feet in dliameter, but
only 1 to 4 inches high; but in general, massive algal crusts cover as much as
80 pemnt of the area. A few isolated heads of Porztes, up to 4 inches In
di~me~ter, occur in protected places, along with large-bhaded Halimeda where
sufficient coarse sand bas been trapped ~n low places.
To the southeast, in front of the wreck and southeastward (Plate 2), the
oidge i,s less well defined, a develapent typical of most of the southeastern
par,t of the hgoon margin. Here the ridge is present, but as rough, channeled
and plrmacled algal susfaces, curving over old coral heads and tossed boulders.
It is not the re1,atively smmth sunface developed in nofihern leeward and wind-
ward strwtwes. It IS awash wibh strong surge and surf and appears as a sur-

RIGBY AND McINTJRE PLATE 3
FIG. 1.-Southwest tip of Isla de Lobos as FIG. 2.-Aerial view of most of Isla de
seen from northwest. Lighter patchy Lobos from the northwest, across the
area in foreground is Diploria clit,osu leeward lagoon. Zonation of leeward
pavement in leeward reef, and darker reef shows well as Acl.opora zone,
areas toward island are patches of algal ridge, and Diploria cliz~osa
Tbala.r.riu. pavement.
FIG. 3.-Boulder ridge at the southwest tip FIG. 4.-Windward lagoon as seen from the
of the lagoon. Hurricane tossed coral lighthouse during a maximum low
heads form the ridge which is capped tide. Tops of Thulas.ria hummocks are
by a small sand ray. The ridge is ap- above water.
proximately 1500 feet long.
FIG. 5. -Crest of eastern end of largest FIG. h.-Windward lagoon at maximum low
boulder ridge. Heads are largely tide with tops of Tbalussiu hummocks
Monfustr,ea and Diploria, now being exposed, as seen from east side of
dissolved and forming the characteris- island.
tic yellow and black zones of a rocky
coast.
BOULDER RIDGE, THALASSIA FLATS AND AERIAL VIEWS OF ISLA DE LOBOS

PLATE 4 RIGBY AND McINTIRE
FIG. 1.-Mounds cd sand tossed by burrow-
ing worm. Arenirolu in sheltered area
north of island and east of spoil pile.
in water less than 1 foot deep.
Mounds are approximately 8 inches in
diameter.
FIG. 3.-Penicil1u.r grove on rocky substrate
in channel south of island. Water is
approsi~nately 2 feet deep, and indivi-
dual plants 2 to 1 inches high.
FIG. 5.-Pewic11lu.r and t~lamentous red and
red-brown algae on rocky substrate in
channel where thin sand veneers the
rocks. Water is approximately 2 feet
deep. Penicillu.~ is approximately 3
inches high.
FIG. 2.--Rippled crest of sand wedge at
southwestern margin of island. Water
is murky and approximately 2 feet
deep. Ripples are up to 4 inches high
and 8 to 10 inches from crest to
crest.
FIG. 4.-Luulcrp~~ cupressoide.r on rocky
substrate in channel at south of island,
in water approximately 2 feet deep.
Some Padir2.1 is attached to exposed
rocky surface. Cuulerpcr is approxi-
mately 2 inches high.
FIG. 6.-Pcrd~nd and filamentous algae at-
tached to tossed blocks on the sub-
merged part of the boulder ridges.
west of the old ship channel, south
of the island. Largest masses of
P~dind are 3 to 4 inches across.
UNDERWATER PHOTOGRAPHS OF LAGOO INAL ENVIRONMENTS ON ISLA DE LOROS

RIGBY AND MclNTIRE PLATE 5
FIG. 1.-Flat-bladed 7'halrrssiu growing in
an undergrowth of Hnlinzeda opuntia.
The large colony of Huliclorzu is typi-
cal of development in the blocked
channel. Individual grass blades ap-
proximately 1 foot long.
FIG. 3.-Thalu.r.ria in sparse growth in
pebble substrate of fragments of Pol-
ite.~ p0uite.r. Darker clumps are col-
onies of Halinzedu opuntia. Individual
grass blades approximately 1 foot
long. Traverse 5, 300 feet.
FIG. 5.-Complex head of Diplorra rlioosa
at margin of pavement with Thulassia
area. Thula.rsia blades approximately 1
foot long. Isolated reef head in chan-
nel north of the island in 4 feet of
water.
FIG. 2. -Border ot rocky, anemones-covered
sandy flats and hummocks of the mar-
ine grass Thalassra, in approximately
3 feet of water. Traverse 5, 250 feet
northeast of the island.
FIG. 4.-Nodular pebbles of encrusting
Lithotharnnium in immediate lee of
windward reef, Traverse 7, 1060 feet
southeast of the island in 2 feet of
water. Rod is one-quarter inch in
diameter.
FIG. 6.-Surface of Diploria rlrvosu pave-
ment in 1 foot of water. Corals, the
algae Halimedu, and crusts of Litho-
thumniunz form the surface. Base of
photograph is approximately 2 feet.
Traverse 7, 1200 feet.
UNDERWATER PHOTOGRAPHS OF LAGO( INAL AND MARGINAL ENVIRONMENTS
ON ISLA f )E LOBOS

PLATE 6 RIGBY AND McINTIRE
FIG. 1.-Small colonies of Arropora palm-
atu, Mnntasrrea rafiernusa and Diploria
rlit~osa on algal-coated bedrocrk near
reef crest, south of island west of
old ship channel. Base of photograph
approximately 2 feet across.
FIG. 3.-Large Ac~oporu palmata colony
nearly 8 feet in diameter in leeward
reef, southwest of tip of island. Water
6 feet deep.
FIG. 2.-Small Arro/lot'u paln2ula head and
smaller heads of D~ploria on crest of
algal ridge on west side of old ship
channel. Water is approximately 5
feet deep. Base of colony approxi-
mately 6 inches across.
FIG. 4.-Tips of large colony of Arropora
pal~tzutu( ?) with small irregular nodes
or conical mounds on upper surface,
in 4 feet of water west of old ship
channel. Base of photograph approxi-
mately 3 feet.
FIG. 5.-Protected northeast side of western FIG. 6.-Montnstvea anwwluri~ head with
boulder ridge southwest of the island. large colonies of the brownish chim-
Skeletal sand partially buries tossed ney sponge, Huliclosa longleyi in
blocks composed of Monrastrea and channel north of island. Base of photo-
Diploria heads up to 2 feet in dia- graph approximately 4 feet across.
meter in 3 feet of water.
UNDERWATER PHOTOGRAPHS OF UPPER REEF ENVIRONMENTS ON ISLA DE LOBOS

RIGBY AND McINTIRE PLATE 7
+%" * All - .*
FIG. 1.--Ac~opora paltnata community at
west edge of old ship channel south
of the ~sland, in water approximately
10 feet deep. Arropora forms the crest
of the reef and Drploria the base. Acropora
approximately 6 feet high.
FIG. 3.-Alont~i.1ired ;rlzrzular~s in typical de-
velop~nent in leeward reef in 10 to
15 feet of water, west of the north
end of the island. Base of photograph
approximately 2 feet across.
FIG. >.-Large colony of P.reudopterogorgi6
arerosa attached to dead coral, now
largely covered with Lirhotharnnium.
Reef slope in front of lighthouse,
south of the island, approximately 15
feet water. Colony 3 to 4 feet high.
FIG. 2.-Upper Acropora palmata commun-
ity near the north end of the lagoon,
in the leeward reef. Arropora rerui-
cornis and A. palnrrrta form the upper
part of the reef over Lithothamnium-
crusted Mnuta.c/rea.
FIG 4.-Lower Acropora pLil?tiurLi commun-
~ty w~th 1-foot head of that specles
capplng algal-crusted Diploria head.
Drplor~a rtrrgosa and Montastrea an-
nularrs forms most of the base of the
reef.
m--
8$.
FIG. 6.-Plexaur~ honr~nulla on algal-crusted
coral with head of Diploria the only
living stony coral. Diploriu head approximately
1 foot in diameter, in
water 10 to 15 feet deep on reef slope
south of lighthouse.
UNDERWATER PHOTOGRAPHS OF REEF ENVIRONMENTS ON ISLA DE LOBOS

PLATE 8 RIGBY AND McINTIRE
FIG. 1.-Millepura sp. and Montastvea un-
nu1ur.i~ in the lower D. .rtr.igosa com-
munity at southeastern corner of the
reef in approximately 40 feet of water.
Individual Motztastre* heads are 4 to
6 Inches in diameter.
FIG. 3.-Montastrea raz~eurto.ru, both alive
and dead, at the toe of the ref and
the margin of the sand flat south of
the lighthouse, east of the old ship
channel, in water approximately 25
feet deep.
FIG. 5.-Montastrea rauernosa sheet with
arms of Comatula(?) at left and
Callyspongia z~uginnlis upright in cen-
ter. Southeast base of reef Locality 38,
approximately 60 feet of water.
FIG. 2.-Mrllepr,id sp. and Monturtre~ rirz -
ernor* In the lowel part of the M.
rat el nos* tommun~ty southeast of the
island in water approximately 60 feet
deep, at the toe of the reef. Local~ty
38.
I I " -
FIG. 4.-Burrowed sand of southern sand
apron in old ship channel area, south
of the island, in water approximately
20 feet deep. Coarse texture of the
sand and reworked surface is typical.
FIG. G.-Montastreu rcrvevno.ru sheet with
Corrzatala(?) and CaIly~pongiu as in
Fig. 5. Same locality as Fig. 5.
UNDERWATER PHOTOGRAPHS OF LOWER REEF AND SAND FLAT ENVIRONMENTS
ON ISLA DE LOBOS
-%

ISLA DE LOBOS REEF, MEXICO 33
f,;ace being etched and at the m e ti'me ~pafiial~ly cwered with algal crusts. Cot:&
are more common hare than in northern developments, perhaps amounting to
40 or 50 percent of the area, and various echinoids are well distributed and
common. Most common corals are Diploria clrvora, D. strigosa, Siderastrea
sidered, and rare massive Porites branneri. Ldlly Millepora occurs in somewhat
sheltered areas. Many soft-My .forms are present in the reef crest as well.
Large anemones and brown sea-squirts are perhaps the most common and typid,
amd hbh occur on the most exposed and on only slightly protected surfaces.
A few colonies of alcyonarians occur locally, but they are squat, low forms.
The leeward reef crest has an even less well-defined algal ridge from the
west of the web1 site, southward to nar the southwestern tip of the lagoon
(Plate 3, figs. 2, 3). Instead of a pronounced ridge, the western side of the
lapon merely slopes gently seaward, and in this transition from the nearly
Llat surfiace of the lagmn ,to the steep seaward slope of the reef front, Lilhothamnium
is an impostant bi,mder and encrusting organism. Locally it forms
as much as 60 to 70 percent of the area, but elsewhere within the same zone
it is 5ar less extensive and most d rhe surface is covered with llving corals.
Perhaps the ce l'kral pant of bhis zone, west of the northern part of the ilsland
and northward for approximately 1500 feet, should not even be included in the
Lithothamnium ridge, even hugh the organism is locally dominant, for the
ridge-l'i~ke structu're is not developed at she reef crest.
A,t tihe nonthern tip of the ilsland the Lithothamnzum crest is as mmh as
300 to 400 feet across, and is a flkt-topped, massive, moderately smooth structure.
Ech~inoids are common to abundant throughout the northern algal fl&,
but c011als are rare. Those prexn~t, usually Dzploria clivora or Siderastrea ~iderea,
form small low heads or crusts, and never compose more than 10 or 15 percent
of ,the area.
Acropora palmata Community
The upper part of both bhe windward and leeward reefs is formed of a
community distinguished by development of Acropora palmala, superimposed
ulpon a base d lmsive or hemispheriaal cords (Plate 6, fig. 1-4). It is w t
well developed in waiter of 15 feet or less, immediately in front of the alp1
ridge or crest (Plate 2).
Leeward development is traceable from south of the sh,ip channel northwad
t~ rhe tip of the 1,agmn and ref. The inner limit of the community is didnguished
by a few comls and cmsidemble Liihothatnnzum crust, but in addition
to bhis 'by bybroad, though low, colonies of Acropora pal~nata. Individual f'ronds
or branches of the colony are aligned normal to the reef trend, and often have
small conid tufts, samewhat reminiscent of the tips of A. cervicornis, at the
tisp of rhe branches (Plate 6, fig. 4). In (shallow water, Diploria clivosa form
sheets around the bases of Acropora colonies and is associated in deeper water
with low cauliflower-like or hemispherical masses of Diploria strigosa and
Montastrea annularis, the latter ,two com~mon in the slightly deeper water in
gmves - or down slope from hhe orest.
W& of the well platfom the shallower part of the Acropora palmata
mmmunlity ifs characterized by a dominance of Diploria clivosa, with minor development
of D. strigosa and Montastrea ravernosa forming a pavement and
undergrowth of headis, capped by heads of Acropora palmata. Acropora colonies
are naaly circular gentle cones rabher then distinctly aligned branches, and some

34 J. K. RIGBY & W. G. McINTIRE
af the Acropora is dead, prticulady at the tips of the branches. In addition to
these dominant corals, Siderastrea siderea, Porites branneri, and broad knobby
hd~s of Millepora are present as accesary organisms, dong with crusts of
Lithothamnium, red and punplish echimids, bring sponges, date-pencil urchins,
bright red and purple mkunicatm, brown anemones, and colonies d the algae
Halimeda, Caulerpa, and Penicillus.
The outer deeper part of Acropora community development is distinguished
by greater relief and with larger, higher heads of most of the corals. Diploria
clivosa gives way to Montastrea annularir as the dominant coral at the base to
bhe reef, but is still present with others as a minor form, accessory to the main
reef mass. Colonies of Acropora palmata grow as moderately large, but high,
tree-like forms whose upper crest gradually lowers as the community is traced
seaward, unti'l in water approxilm,tely 20 feet deep, mad Acropora growth
stops. The outer limit of the cmunity war, mppd at that transition.
Relief is much greater in the outer zone, for groom sepamting the coral
heads are deeper and are often chwked with rolled logs of Acropora, fragmenbs
of Montrutrect and other coral heads which litter the gullies like a log jam.
Acropora is a relatively milnor, but distinctive, part of the outer part of the
mne. It forms less than 20 percent of the area. Most of :he reef, perhaips
locally as much as 60 percent af the area, is composed d large heads of Montartrea
annularis, with Diploria rtrjgosa and Siderastvea siderea each forming
as much as 10 percent of the area. Porjtes, Meandrina, Mussa, and Agaricia
are a111 present within bhe co~uni~ty, but form a minor volume, as does
Montastrea cavernosa, hhe species that forms much of the reef toe in b&h
windward and leeward reefs. Millepora is present as a bladed form in the lower
part of the tone, while the genus takes on a knobby massive form in the shallower
part of the inner community development.
~bsemations on the windward Acropora community are more limited became
of the constant sunf over ~bhis part of the reef. However, the upper or
inner ,part of the cornunity ms studled in three localities, and the lower or
outer part in two areas. In mast respects, the windward reef fauna is sim~lar
to that of the leeward mf wi,thi,n the Acropora community, with the exception
,that Montartrea plays a minor rol~l (in windward reefs and i'ts place 1s taken by
msive heads of Diploria strzgosa, 4 to 6 feet in diameter. The latter species
mposes 50 to 60 percent of the area in both inner and outer parts of the
community development. Two forms of Acropora palmata are recognizable,
as in lee reefs-one form with conical mounds and an almost A. cerv*~ornzs
upper surface and distal margin ho the branches, and the other form h a
smooth upper surface and with blunt ends to the fronds (Plate 6, fig. 3). The
farmer m r s high on the reef front and characterizes the inner zone, and the
&her in water slightly deeper, down to bhe owter limit of the community.
Calonies up to 8 feet in diameter and equally a high occur in water approximately
25 feet deep. In 'bth forms branches are strongly aligned normal to the
red front. Crusts of Lithothamnzum are significantly deeper ~n windward community
development, where they are common in water up to 30 feet deep.
Montrslrea annularrr Community
The Montastrea annularrs comm~nii~ty
is developed in the leeward reef in
depths of from approximately 20 feet down to ~approximtely 50 to 5 5 feet. It

ISLA DE LOBOS REEF, MEXICO 35
grades lagoonward into the Acropora palrnata community by appearance of that
coral, and downward into he Montastrea cavernosa communiity where that
form becomes the dominant coral in the fabric. Bt has been mapped from the
old ship channel at the southern enld of the island, around the southwestern
tip of the lagoon, then northward to the tip of the reef and lagoon (Plate 1).
Throughout its development kt is characterized by dominance of Montastrea
annularis, with other hem~spherical or massive corals present but quantitatively
less mportant.
In the southern development, Montastrea annularis composes as much as
40 to 50 percent af tk area, wiith Drploria strrgosa, D. labyrznthrformis, and
Montastrea cnuernosa less common. In water 20 to 30 feet deep, gigantic
isolated coral heads up to 15 feet in dilameter and up to 20 feet high form
buttresses between somewhat irregular grooves. Montastrea annularis fom
yellowish green, cauliflawer-type colonies and Dzploria spp. forms massive
hemispherical heads hat are cha~acte~iwtically .tan or yellow gmy-brown with
color most intense in depressed pafls af tihe skeletons. Montastrea cauernosa is
presen8t as sheet-like and masslve hemispherical colonies which appear medium
gray-brown from above.
West of the island, oppi,te the high spoil piles, Montastrea atznularis
forms massive colonies that compose up to 75 percent of the reef (Plate 7,
figs. 3, 4). The remainder of the reef is mainly Montastrea cavernosa and
Dzplorza labyr/nthzformis (?), babh of which form sheets in addition to the
normal hemimsphesical heads. Sheets are mast commonly developed along the
sides of well-defined, deep grooves and broad channels. Here the whole zone
is alive, with little algal enc~~hatiion. Lithothamnrum is present, but in mirmr
amounts and IS not a distinctive ,binder liike it i8s higher in the reef. One gets
the imprwion thsat below approxi'mately 30 feet, the fabric of the reef is much
mox open. This, of course, recaches its maximum development near the toe of
the reef in the Monta~trea cavernoJa communi,ty where an open cavernous
fabric is typical. This is probably related to reduction in binding done by
Lithothamnium, so that lower zones are more porous.
Dlplorra stvigosa Community
The Dzplorza stngosa community is developed along the windward margin
af the reef, and is gradational 'below the Acropora palmata and hve the
Monta~trea cauernosa communities. It is mappable from east of the old ship
channel, south of the island, eastward and northward to the northern tip of
the reef and lagoon (Plate 2). It 1s one of the broadest developed communities
within the reef and is approximately the equivalent of the Montastrea com-
munilty developed within the leeward reef.
Only the upper part of this zone has been studied because of the vigorous
sud an bhe windward side of the lagoon, but the community is distinctive. It is
separable from the ,shalher Acropora zone because that distinctwe pus is
want~ng in dl water deeper &,an approximately 25 feet, and separable from
the lower Montartrea cauernosa community kause that form is dominant only
in depths greater than approximately 55 to 60 feet.
sassive hemispherical or sheet-like developmenlt of Diploria strigosa, D.
cliuosa, D. labyrinthif ormrs ( ? ) , Siderastrea srderea( ? ) and Montastrea annu-
/ar.is is typicall of the zone. D. .rtrigo.ta comprises as much as 50 percent of bhe

36 J. K. RIGBY & W. G. McINTlRE
area, with D. rlivosa and M. a'nnularis each coverlng perhaps as much as 15
percent. Szderastrea sp. and M. cavevnosa are relatively rare within the zone, as
are heads of Millepova.
Deep, narrow channels are developed throughout the zone and most are
floored with coarse coral debris. The channels apparently broaden and become
sand flood in bhe lower part of the zone in approximately 40 feet of water.
The fMontastrca cavernosa mmunilty is well developed at the toe of bath
windward and leeward reefs of Isla de Lobos. I,t is the lowermost cmun~i'ty
stdied, akhough bhere may be d'eaper coral development In the rcxky area norrheast
of the Islra de Labos reef. The community is developed in water from
approximately 55 or 60 feet dawn )to the base of the reef at depths of 75 to
80 feet deep at the margln of the surrounding sand apron.
This community was studied in three separate localities (Text-fig. 2)--one
locality along the margin of one of the large flat-bottomed grooves typ~cal of
the leeward reef west of 'the well platform, and at two localities east of the
old ,ship channel and southeast of the island, at the southeastern tip of the
windward reef.
Windward development of the communiity was stud'i~ed in 65 and 75 feet of
water at the toe of the reef at the margin of the flanking sand apron. In both
areas where dives were made, most of the living corals are hfonta~trea cavernosa,
which forms broad, brownish gray sheets and low, hemispherical heads which
cover approximately 50 percent of the area (Plate 8, figs. 2, 3, 5 and 6).
In many areas ~t appears as a thin sheet whjich spreads, frosting-like, over older
rds and dead had's. Diplona labyvinthzfovmr~ accounts for approximately 10
percent of the area. Other conals are mlnor and cover, as a total, less than 5
percent of the area. Included are a slderastnid form, Agarrcra fragzlis, Mussa
cdngulosa, and Madraczs sp. The latter forms knobby rnasses on the shadowy
underside of heads and sheets, but the other species form Isolated heads or
colonies.
Head's of corals rise from a few inhes ,to as much as 8 feet directly f m
the sand apron. The enstire reef toe IS exceedingly cavernous and appears like
hollow, hemispherical heads balanced on ~solated tips. It gives the impress~on
af being at least half voids between and under heads. In many areas there
are ,openings large enough to crawl or look in~to for 30 or 40 feet under arched
heads and crusts, now gen.tly suspended on (arched f ~ngers. One can easily see
how great heads could !be readily torn loose from bhe cavernous structure and
tossed high on the reef. This is the part of the reef which could be sufficiently
porous, even after being filled with calcareous sand, to be a significant reservoir
for petroleum, particu1,afly w!hen sealed with the nearly impervious Upper
part of the reef which various authors have described.
The alcyonarians Eunicea (Eldnzceopsis) clavigercl and E. (E?~nzreopsis) calyculata
roronata are relatively common attached to dead areas on rhe reef or to
only slightly buried dead blocks out a short distance into the surrounding sand
flats. They are probably at their greatesmt development whin this zone of the
reef.
Bcight orange crinoids, Comatula(?) sp., are distinctive organisms present
only within this community (Plate 7, fig. 6). They are common In most

ISLA DE LOBOS REEF, MEXICO 37
crevices or under most shadowy edges, extending only the grasping, bright
orange, feathery pinnate arms for food, some reaching 8 inches above the rocks.
In same areas t.here are 6 to 8 individuals per square meter, and more d d
~robablv have been Dresent had more suitable. dark. ~rotective crevices devel-
1 ' 1
oped. In most areas, however, 2 or 3 per square meter is typical.
Two species of Cdulerpa, a broad-)bladed Ikte form and a small greengraped
species, and some ,brown flat-laved dge are common In the lower
part of the zone, particularly wihere sand has blanketed racks a fraction d an
~n& thick. Caulerpa is most comn in the slightly sandy areas.
Leaward observations were made at the toe of the reef in water 75 f&
deep, west of the wdml plakform, di,rer;dy out from the large marooned tree
stuck on the reef crest. The reef here rises olmt vertically for the flrst few
feet, and then assumes he normal gently rising @tern toward the lagoon.
The most daminlaat cor.al in this lower reef community is Montastrea
cavernora. Imt is the only living cod in the lower 5 or 10 feet of the reef where
we saw ist, and is the dominant form in the lower 20 to 25 feet of 'the reef as
a whole. It forms sheets and hemispherical heads, as in the windward reef. In
addition to Montaskea, Madracis is common and forms lumpy areas several
feet across, appeaoing like massive Porztes thickets. Mt~rsa angulora, Agaricia
fragzlrs, Porztes bvannevi( ? ) , and Siderartrea( ?) sp. are all important, though
not dominant, corals a few feet above the sand-reef interface. The latter species
all increase upwards, so that at the base of the shallower Montartrea annularis
zone, they are wen more common, alt'hough ytill not dominant in the reef
fiabnic.
Crimids are relatively rare, and alcyonlarians were not seen in leeward reef
develaament. Ocul~na was col'lected onlv from here. and some cheilosbmous
1
bryozoms are al,w common with Madracis in shdowy areas. Oculrna is growing
In shadows, expanding the colony downward.
Sponges are essentialily ,the same as in windward development, but are less
robust and more widely spaced.
The general fabric of bhe reef is nearly as pornus or cavernous as in windward
development, but here deeper openings are mainly filled with fine mlcareous
debris. Coral heads are not as large, ahhough individual head,s seem
to be doing well. More dead-looking, algal-crusted, coral material is present
here than windward, and many of the gullies that feed into the large flatbottomed
grooves are filled with sand and gravel. Fine sand and silt are burying
the base af the reef tm, abviou~ly lapping around the coral heads and up onto
bhe reef, tike small1 jalluvial hans. The latiter lareas slope relatively steeply away
from the reef to meet the flat bottom of the gully or groove a few feet away.
Most of bhe calcareous sediment has apparently been passed down through the
reef structure rather than over it. The upper parts of bhe coral hds are
relatively clear of debris while the lower areas are obwiously flanked by sediment
oncly recently in transport, so lighdy consolidated that minor turbidity currents
are generated by slight digging into the unstable slope.
Ebth windward and leeward reefs in the vicinity of Isla de Lobos are
apparendy composed of la lower open and cavernous structure, which may or
may not be filled with calcareous sediments washed into &he structure from
above, and an upper more firmly cemented tone. It is with,in the upper zone
that most workers have studied in the past, and hence bhe concapt has developed
:hat all reefs are solidly knit structures. In the Lhs reefs, however,

38 J. K. RIGBY & W. G. McINTIRE
only the upper hLf appears to k f.irdy cemented w,irh bindimng organisms Yuch
as algae. In the lower half of the structure most binding is done by lateral
growth af cam1 heads, and this only sufficient for support during noml
growth. During periods of intense, deep storms large heads are obviously
ripped bse an'd tossed hut.
North Channel Community
A mderately deep channel was developed in the otherwise shallow 1,agoon
mrbh of the island prior to constmction of the sh~ip ahannd and causeway. It
is o b n as a distinct facies or cu>mmunity on the map (Plate 2) because it is
a reef-firont assemblage, isolrtted within the shallow grass-covered lagoon.
The channel extends approximately 175 feet east af the causeway and is
perhaps twice that wide parallel to the spoil heap. On the three sides away from
bhe causeway the chan'nel shal~lws and is floored wilbh dead coral heads a d
Lithothamnium-ccrated pavement to the margin where shallow Thalassia hnks
hit the coral growth. Since construction of the causeway and diversion d
lagoon waters northward around bhe we181 platfom, the channel has been fillling
with soft, fine-grained sediment and the earlier established coral community is
mw bei,ng redwed.
The aknnel is presently cut ina two segments by the spoil heap and ship
channeldne west of the high protective mound opposite the docks, and the
other east of the causeway and mrth of the idand. In both, large flat-tapped
heads of corals have developed up to low-tide level, and are now growi,ng
horizontally. Montastrea, Drplorra, Meandr~na, Porztes, and Srdera.rtrea are
present in both segments and form heads up to 6 feet high and as much as 8
or 10 feet in d~arneter. The upper surface of most heads 1s now crusted with
Lithothamnium or blanketed wioh f ine sediment ia which Halimeda is growing.
Vertid or overhanging sides d the hds are still dive, and isolated masses
seem to be doing well in spite of the highly turbid, quiet water. Some hemispherical
heads and remnants of older algal-crusted heads are developed in
the eastern segment.
Montastrea annularis is the dominant form in the deeper water, and forms
the most conspicuous heads and flat-topped thles. Diplorra clivosa, Meandrina
meandrina, and Porites wdnneri are all present in varying proportions and are
more common than Montastrea along the northorn part af the eastern segment.
Most Porites head's are on the rocky floor of the channel, but some have
plimly perched on top of the flattened heads, as though they have been
able to survive in an area where other corals have been killed. They are noticeably
out of place.
~edand black urchins occur itn the crests and along the flanks of the coral
haads. Diadema occurs more rarely. In addidon to urchins, many large cl~~ps af the sponge Halzclona iongleyi .are growing on the corals. Heaps of &dl
debriis occur below some coral heads at entrances to openings now occupied by
octopi.
The floor of the depression is blanketed by a th'ick mat of Thalasria with
clumps of Halimeda spaced here and there in 'the grass. Both grass and the
rocky base are now veneered with fine silty sediments, much of which is
highly organic immediately beneath .the oxygenated surface. There is considerable
dead Thalassza blanketing the sides of the spoil heap and in the deeper

ISLA DE LOBOS REEF, MEXICO 39
areas of the channel. Construction of the causeway has obviously interrupted
bhe normal sedimentary and faunal pattern of the area.
Dead and Channeled Area of Reef
The area west of .the island, :but sourh of the newly dredged ship channel,
in the vic~nity of t'he boulder ramparts south and southwest of the island, shows
marked reduction in reef development, at least in the upper part of the area
where coral growth might be expected.
Coral growth 1s restricted sourh of the boulder ramparts, particularly west of
bhe deep break in the reef marki'ng $he old ship channel. Lithothamnzurn, a
pink and light purple encrusting form, has blanketed all the upper part of the
reef mass, and has welded the top of tihe reef into a solid structure which is
now beisng bored by various organlisms. Worms are common and various species
of echinoids, particularly brownish red and reddish purple Erh~nometra lacunter
are common. In some areas they occur 20 to 25 per square meter in both
exposed and sheltered slopes of the algal pavement.
Millepora is present, but in limited development. It forms tan, low and
encrusting masses, with bi'nger-like vertical tips as much as an inch long, often
light gray-'brown at t8he terminus. It is functioning as a binder, somewhat like
the algal pavement, but occupies less than 5 or 10 percent of the area.
- -
Acropora palnzata occurs as isolated, often stunted heads in the Lithothamnium
area, locally growing in up to 8 or 10 feet of water. These are isolated
heads 5 or 6 feet h,igh and of approximately tthe same diameter, and are spaced
tens of feet apart in front of the boulder ridge. Irregular growth of this species
characterizes a part of the reef whidh seems to have suffered by restriction of
cimlation .related to the boulder ridge. The massive hemispherical heads of
D~plorza strigosa, D. rlivosa, Montatrea annularzs, and Montastrea cavernosa
which form the lower parts of the reef are affected only in their upper growth.
They are here dead and crusted by pink masslve algae, even though eI,smhere,
away from the boulder area, they grow to near the law-tide level in some profusion.
West of the large boulder area, at the southwestern tip of the reef, the
upper pafit of the reef is similarly mainly a dead coral region, now being
crusted with calcareous algae. Remnants of the Diplorla clzcosa pavement are
evident among the boulders, for D. clivosa and Montastrea alznularis form small
heads, generally on the western sides of bouldery masses, for a few feet away
from he base of the boulder ridge. To the north, however, even thew more
hardy specles are dead and algal crusted, or are now mainly buried by sand. The
ech,inoids, Echinometra lacunter, bolth red and black forms, and Diadema are
common In the cavernous upper surface of this region north of the western part
of the boulbder beach.
Northwest of the boulder area, from a depth of approximately 3 feet outward
to at least 15 fed, the upper surface of the largely dead reef ,is only a
veneer of Lithothanznizrm now being bored by echinoids. Boring sponges, mainly
a brick-red, coarse-textured Cliona, are common in overhanging areas along the
upper dead part of the reef. Red, purple, and brown tunicates are also common
in protected places.
Most of the corals which are present develop relatively small heads, usually
less than 1 foat in d~amater. Most prominent species, in water less than 10 feet

40 J. K. RIGBY & W. G. McINTIRE
deep, are: Dzploria clivosa, which forms flat knobby heads up to 1.5 feet in
diameter, Meandrina sp., Porites porites, Siderastrea siderea, D. strigosa, and
Acropora palmata. Combined area covered by corals is less than 5 percent of
the surface. All hemispherical forms appear to be a reppulation, for hey are
growing discordantly over algal crusts which in turn have deveIoped on top
of the main dead coral mass. Same Acropora palmata colonies seem to represent
repopulation as well, for the species forms very small, low palmate colonies.
The near "desert" conditions of the reef flat and immed~ate seaward part
of the reuf was possibly produced by restriaion of circulation by the boulder
rampatt to the southeast, for it cut off most wave action generated by prevailing
winds. The reef crest is now ~bthed rnainIy by sedliment-laden lagoonal water
that streams past the south end of the island between the spit and the boulder
ridge. It is probably nutrient p r and hu reduced oxygen content as well.
Killing d the upper pa^ of the reef is probably not related to dredging to the
north, for reppulation seems older than that activity, judging from the limited
effect on corals closer to the ship channel.
Toward the north, beyond the area shadowed by the boulder ridge, cords
are less seriously affected, so &hat from 500 to 600 feet north of the western
end of the boulder ridge, more normal, leeward reef coral development can be
seen. Icn this region Diploria clivosa covers as much as 70 to 80 percent of the
surface near the reef crest, with only minor areas of Lzthothamnzum crusts.
Cmal heads are large and rise as much as 2 or 3 feet above pockets af sand
where Poriter porites, Siderastrea siderea, Halrmeda, and Penicillus seem to be
doing well.
Most serious retard'ation of the reef in th~s northern area is seen on the
seaward slope, in water 10 to 15 feet deep, where as much as 90 percent of the
area is now crusted by Lzthothamnium. Corals are only minor in the present
community fabric, even ihough the dead rocky base consists of large heads of
Diploria and Montastrea. In this area Acropora palmata, Dzplora clivo~a, and
D. strzgosa are the only surviving corals. Leeward tips of Acropora fronds
are dad, but wind,ward tips are still almive in many colonies, particularly where
the colonies are aligned i,n a northwest-southeast direction, normal to the reef
edge.
Buttresses and grooves are well developed in the red mass, wen in the dead
area. Diplo~za cl~vosa form the base and sides of buttresses now occasionally
capped with clumps of Acropora. Montastvea and Porites are present, but as
accessory to the major fabric. The ch'annels are deep, straight-walled grooves.
Many have abrupt begin'nilngs and terminahons 10 to 15 feet high, but others
taper near the reef crest much like subaerial streams.
Immediately ~outheas~t of the boulder ridge, west of the old ship channel,
deep grooves ,and channels are developed in front of the ridge crest. Many are
3 to 5 feet wide and up to 20 feet deep. They deepen seaward between vertical
walls of living Diploria strzgosa and dead Dzplorza and Montastrea, now
Lithothamnium coated. Troughs of these channels are commonly sand-covered,
often rippled, for bh~s is an area of active sediment transport.
Gullies west and northwest of the wes'tern edge of the boulder bed are
oriented roughly normal to the reef edge, but with an irregular, almost anastomosi,ng
pattern on all but the highest part of the Lithothamnium ridge. These
depressions may be Ilnear, ,irregularly circular, or irregularly arborescent around
some of the now planed coral head's. The gull~es are commonly floored with

ISLA DE LOBOS REEF. MEXICO 41
smooth algal crusts, but in addition, often have coarse blocks or cobbles of
corals in depressions. There is little sand in the area and practically mne in the
gully troughs. As individual troughs are traced westward from the red margin
into deeper water )the gullies form a more regularly oriented and spaced systa.
It is about at this depth that the coral growth berms more normal as well.
SURROUNDING DEEP-WATER HABITATS AND COklAlUNITIES
The reefs of Isla de Lobos, Medio, and Blanquilla rise from a sand-veneered
plabform along @he eastern coast, and within this relatively deep-water environ-
ment, many habitats a d c0mm~uni:ties could probably be differentiated. Our
sampling is not sufficiently dense to al,low more than braad general,izations,
such as those presented in the section on topography. Additional work is planned
on this aspect of the reef complex in coming years.
GEOLOGIC HISTORY
LATE LAGOONAL HISTORY
The spil piles and margin of the dredged ship channel give an unusual
opportunity to study the upper part of the reef flat across mast of the lagoon.
Much af the spoil appears to have been moved little after the initial dredging,
heme any zonation in the spoil might be si,milar to that within the bedrock of
the is1,and and give some clues to the development of the lagoon flats.
Large fcagmen'ts of Diplorra and Montartrea, two corals common in the
leeward reef, dominate #the dredged fauna in the vicinity of the flare, at h e
southwestern end of the spoil pile near the entrance to the ship channel. Mont-
cartrea annularis, Diploria clivosa, and D. strigosa, with minor amounts of
Pontes wanneri(?), form ,the coarse material exposed on the washed channel-
ward face of the spil pile from near #the flare to within 300 feet of the Pemex
dacks, approximately 550 feet to the northeast.
Acropora palmata logs are 6irst apparent in the spil approximately 300
feet sauthwest of the dlack fiacilities and b m e more common in the spil
toward the dds. Acropora iss a major element of the dredging throughout
the remailnder of the spoil pile, until near the well platform where coarse debris
is not ev.ident and much of the pile may have been transported.
Throughout much of the spoil pile, northeast of the island and dock area,
@here is a lower zone approximately 2 feet thick in which Dzploria clivosa and
Montmartrea annularis are the dominant coral species present, but abve this
lower zone, Acropora palmata fragments dominate. This is particularly well
shown near the bend In the spoil heap, 1200 feet north of the isl'and, on the
channel side of the rdway. This rehtionshi~p suggests that Diploria and
Montastrea occur above Acropora in bedrock of the island.
The largest dredged fragments visilble no& of the docks are of Acropora
palmata and aange up to 4 or 5 ,feet in diameter, and up to 7 feet long. Most
fragments of this and other species are smaller, usually only half this size. All
fragments af Acropora are coated with Lithothamnium crusts, so that in some
specimens an algal crust as much as 3 inches thick had developed. In addibim
to being enlarged by calcareous algal crusts, some Acropora masses are over-
grown with Agaricra fragilis fronds, then covered w,ith algae. There is nothing

42 J. K. RIGBY & W. G. McINTIRE
Ship Channel
TEXT-FIGURE 9.-Diagramatic cross section of the margin of the ship channel showing
possible zonation. 1. Halimeda sand in which Thalassia acts as a sediment trap; 2.
P0rite.r poriles gravels associated with algal oncolites; 3. Arropora palmda and
associated hemispherical corals; 4. Montas~rea and Diploria. Vertical zonation is
based upon an inferred relationship interpreted from sequences in spoil from the
ship channel and observations of the upper part in the cut edge of the channel.
Not to scale.
evident within the spil heap suggesbive of a unninunity older than an Acropo~a
one in the gross - pattern of reef development.
Fine sediment and ruble, mainly Poriies fragments and mollusk shells mixed
with drilling mud, have been cleaned from the dredged channel and heaped in a
pile approximately 6 feat high on top of a graded surface southwest of he
docks. This accumulation is unquestionably not related to original dredging
but represents fine pble and cobble-sized material swept into the channel
later. The association is typical of Thalassia grass flats developed at present to
the northwest, suggesting that bhe debris was washed in during severe winter
storms that sweep in from the northwest, driving waves in over the lagoonal
flats into the ship channel from bhe normally leeward side of the lagoon.
It is unfortunate that walls af the ship chanlnel are now thickly veneered
with sediment derived from the lagoon, mixed with drilling mud. One can then
only ilnfer a stratigraphic relationship based upon an inverted sequence in the
spoil and u p limited observations of the upper part af bhe breached grass
flats at the margin - of the channel.
Using this type of evidence, one can observe that the present-day ThaIassia
fliats are developed upon a surface of Porites fragments in walls of the channel
near the well site. Ln several cuts, north and west af the platform, a gravel
layer up to one-foot thick of Porites fragments is developed below the Thalassia

ISLA DE LOBOS REEF, MEXICO 43
cover and obviously antedates the grass in an ecologic succession (Text-fig. 9).
One can infer from the spoil heaps that the Poriles gravels are built upon
a sequence of Diplorra clivosa and Montastrea annulavis (Text-fig. 9), whioh
in tulrn is built upon a sequence in which Acropora palmata is the dominant
species. Thickness of hex latter sequences cannot be determined with the in-
formtion at hand. Judging from abundance at any point, however, the
Diploria association seems to be thickest toward the leeward edge of the lagoon,
and probably thins to only a few feet in the Interior of the lagoon.
BLANQUILLA REEF
Blanquilla Reef is the northwesternmost of the three associated reefs south-
west of Cabo Rojo and Tamiahua Lagcyon (Text-fig. I), and is the inkr-
mediate one in size. It is an elliptical reef, approximately 3000 feet long in
a northwest-southwest direction, and approximately half that wide. It is a flat-
topped reef, with a shallow lagoon corn letely rimmed by active growing reef
communities. Unlike lsla de Labs reet there is no island above high bide,
but two small areas of coarse, rounded gravels are developed in the lagoon. One
is a compound spit-like accumul~ation in the south central part of the lagoon,
in approximately t,he position of Isla de L ab within the reef flat there, and
bhe other in a more cent,ral position and much lower. The central gravel bank
is not exposed at low tide, but the larger south-centaal one is approximately 2
feet h,igher and is exped d,urimng extreme low water.
LEEWARD REEF
Reef development is similar to that at Isla de Lobes. The leeward reef har
an outer Montastrea-dominated community hat extends down to at least 20
feet, the lower limit of our observation. A camunity dominated by Acropora
palmata is developed in front of the reef crest in shallower water, where large
smooth margined, circular colonies, up to 6 feet tall, grow to near the low-tide
limit. At bhe outer margin of the Acropora community, the surface is approxi-
mately 80 percent live coral, either Acropora palmata or Montmtrea with minor
areas of Dzplorra clz~osa. Such development conkinues to near the Litholham-
nium crest where most coral growth stops abruptly and all but approximately
20 percent of the area is crusted with algae. As one approaches the algal-
crusted area from the lee s~de, Acropora palmda colonies are much shorter and
commonly dead, particularly at the tips of fronds. A few small colonies of
Acropora cervjcornis are present in the upper shallows in front of the algal
ridge, but are not present on the ridge or in deeper water. Hemispherical corals,
like Dzplona strzgosa, become low, plate-like crusts and many have dead interiors
so that they form small micro-atolls, and finally disappear from the community.
Diploria cliz~osa forms irregular sheets intersprsed with major areas of algl
crusts in water from one foot to only a few iruches deep at low tide. As the
ridge is approached, corals become rare and the entire surface is covered with
ptnk crusts of Lithotbamnrum.
There are some weak, irregular, radial grooves on rhe seaward crest at the
base of the algal ridge, but most grooves are larger and more definitely defined
in slightly deeper water. Straight-walled, narrow, cavernous openings up to 30
feet deep occur as seaward extensions of the grooves in the ridge and the
meandering, ditch-like grooves in the Acropora palmda zone. In some instances

the gmves have been b~idged w,ith corals toyproduce an intricate, very narrow
depression, inches across but feet deep, or an open, cavernous reef mass. Where
the grooves are wide they are floored wi'th coarse coral debris. Sand is rare,
even in he i,ntedior of bhe lagoon, an,d must be swept off the reef into deeper
water or hi~dden withi'n the open porous rmf at depth.
The Lithothamnium ridge is a strong, well-defined feature along the west
side, up to 200 yardls moss, broken only at the southwestern part where it
kames irregular and weak, somewhat Ifike the leeward ridge on L b . Here
coral heads lap far onto the flat-topped reef, and shallow grooves cut in,to the
rnargi~n of the lapon. Isolated heads of Diploria clzuosa cxcur in low SF,
along wlrh many redd,ish brown and purple echinoids, and are the main orgsn-
ism of the fl,at other than the algal cmst. Even in areas of maximum cod
development, however, they cover less than 15 percent of the area. Many isolated,
tossed, dark gray-brown heads of corals have accumulated on the crest of the
reef, particularly at the nofihern and western margin of hhe flats. Most are
Iudged on the bordering algal ridge.
LAGOON
Algal crusts grade lagoonward from the masslve, sheet-l~ke surface of the
reef crest into rounded knobby pebtrles immediately behind the reef. This
pebbly development covers twethirds of the flat lagoon bottom around the
outer margin. Pebbles are formal of algal crusts over Porztes porites fragmenks,
snail a d pelecypod shells, and some are compound oncolikes of algal masses.
Pebbly algal oncolites grade into intermixed, arborescent, algal structures
and pebbly masses in the inner third of the lagoon. Locally arborescent masses
cover as muah as 20 percent of bhe area, and are interm~xed wi.th oncoli,tes, a
few conal heads, and patches or thickets of a weed-like tan algae. The associab~on
1s developed within trhe lagoon interior, parhicularly away from the pebble
bans, where the water 1s up to three feet deep even at very low t~des.
Iisolated heads of conals are developed within this pebbly facies, but never
cover more than 10 or 15 percent of the immed,iate area. Sideratpea radians
and Porites porztes dominate as heads only a few inches high or in diameter.
They form fragmenks around which many of bhe algal pebbles grow, and are
most abundant 300 to 400 feet in from the leeward edge, where the water
deepens to as much as 3 feet at low tide. Corals are also moderately common
east of the medial gravel bar, where heads up to two feet were notated. Most
heads in the eatern part of the lagoon are Diplorza rliuo~a, but a few herads of
D. strigosa, Meandrina, and a mmai~ve Porites also occur.
Diadema and okher echinoids are common across bhe lagoon flat, associated
wi,th nearly every head or irregular Lithothamnzum crusted root of a had. A
few, large, white echinoids, noted only in the Thalassza flats on Lobos, also occur
in some of the quieter water. Tjhe llight-gray forms are rare, however, particularly
when compared with the black, long spined Diadenza, or the reddish
brown and purple-black Echznometra lacunter, forms which occur not only within
the lagoon, but throughout the algal ridge and seaward slopes or the reef as
well.
P&bles are the secbiement af the lagoon. The lagoon is swept free of fine
sedfiments, except in bhe immediate lee of m e of the broader coral heads and
of same of the gravel accumulations, where bidastic sand is acmulafiing. In

ISLA DE LOBOS REEF, MEXICO 45
sevenal of these protected areas, sandy patches are forming up to 2 feet across
and in some of these, a light tan, knobby holothurian is very common. In one
area of maximum development 70 holothlunians were counted per one meter
square, but most sandy areas are more thinly populated. These edhinderms
were grating upon fragments of a tan weed-like algae, fragments of which
form m t
of the sand in the area. Holothutrims were not seen outside the
smll sandy patches.
Small gravel bars in bhe intefiior are composed of rolled algal pebbles, now
rounded and with packi'ng suffiiciently loose that walking across the bars is
difficult. They form with a moderately steep western or leeward margin and a
more gentle eastern margin, preisdly because of shaping by waves, driven
across the windward reef flat by prevailing winds. These i,nterior bars are
estimated to be from 50 to 200 feet wide and as much as 400 to 500 feet long.
They separate shallow water of the western part of the lagoon from slightly
deeper water of the eastern flabs.
WINDWARD REEF
The wlndward Lzthothamnzum-coated reef flat is as brd as the leeward
one. It has a diut~inct inner margin two to three feet high, shaped like the lee
of a dune, although it is now ~Lidly bud by encrust~ng algae. The flat was
constructed of tossed pebbles, welded toge+her to form a wave-swept platform
now buried by only a few inches of water. It is withlin a slightly deeper moat
behind the algal flat that most of the observed sand is accumulating.
The windward reef was not observed in any detail because of rough surf,
but it appeared, in huruied travenses, to be formed in the upper part mainly of
Dzploria stngosa and Acropolv palmata, like the windward reef of Isla de
Lobs. Lower zones were not observed.
Thalassia and its associated fauna are not present on the Blanquilla Reef,
presumably because a suitiable surbstwte its l'ackimg. Development of a Thalassia
cover seems the next step, however, if sufficient sand an accumulate.
At the time of our bnief visit, Pemex hmd placed a dredge new the Whesn
margin of the gravel bars in the interior of bhe lagoon, presumably in preprab~on
for dredging a sh,ip channel to serve a planned well site.
MEDIO REEF
Mdio, or M~ddle, Reef ims &e cent,rd reef af the three closely associated
with Isla de Lobos. It is also the smallest of the three. Medio Reef is approximately
2 miles northwest of Isla de Lobas reef, and 2 miles southeast of Blanquilla
Reef. Like Blanquilla it lacks a cay, although now Petr6leos Mexicanos has
const'nxted a large concrete well plabform on tihe structure. Little time was
spent on Medios, and no time in the water investigabi'ng reef and lagoonal development.
However, from limited observations one can recognize a well-defined
Lithothamnium ridge and windward a d leeward reef development around a
shallow lagoon. The lagmn is now breached wi& a aship channel dug to serve
the well platform. The channel extends nearly khrough the I'agoon f m
leeward side to wi,thin a few tens of feet of the reef crest on bhe windward
side. The channel cuts the larger part of the reef structure on the east from
the smaller pointed part of the reef on the west, the side where the well site
i's s i,~ed.
the

The reef at Mdio has much more in common with that at Blanquih
than with the larger one on Ish de Labs, for on both these smaller reds
strong waves surge completdy across bhe lagoon. On neither is there a sandy
lagoon capped by Thalcassia, but on both, isolated coral heads grow attached to
a rdy substrate in water a few feet deep. Acropora and Montastrea colonies
are recognizable thmughout the 1,agoon and in bordening reef tracts near low
tide. Litde else was differentiated from the very superficial look at the reef.
REFERENCES CITED
Klovan, J. E., 1964, Facies analysis of Redwater reef complex, Alberta; Bull. Canad.
Petrol. Geol., v. 12, p. 1-100, pls. 1-9, 20 text-figs.
Korn~cker, L. S., and Boyd, D. W., 1962, Shallow-water geology and environments of
Alacran reef complex, Carnpeche Bank, Mexico; Bull. Amer. Assoc. Petrol. Geol.,
v. 46, p. 640-673, 34 text-figs.
Mobius, Karl, 1877, Die Auster und die Austervlrtschaft; Berlin (Translat~on, 1880,
The oyster and oyster culture; Rept. U.S. Flsh. Cornmisslon, 1880, p. 683-751).
Murray, J W., 1966, An oil produc~ng reef-fringed carbonate bank in the Upper
Devonian Swan Hills Member, Judy Creek, Alberta; Bull. Canad. Petrol. Geol., v.
14, p. 1-103, 23 pls., 12 text-figs.
Newell, N. D., Imbrie, John, Purdy, E. G., and Thurber, D. L., 1959, Organism com-
munlties and bottom facies, Great Bahama Bank; Bull. Amer. Mus. Nat. H~st., v.
117, art. 4, p. 177-228, pls. 58-69, text-figs. 1-17.
---- , Rigby, J. K., Whiteman, A. J., and Bradley, J. S., 1951, Shoal-water geology
and environments, eastern Andros Island, Bahamas; Bull. Arner. Mus. Nat H~st., v.
97, art. 1, p. 1-29, pls. 1-8.
Thorson, Gunnar, 1957, Bottom communltles; rn Treatise on marlne ecology and
paleoecology, Volume 1, Ecology; Mem. Geol. Soc. Arner. 67, p. 461-534, 20 text-figs.
Wells, J. W., 1957, Coral reefs, in Treatise on marine ecology and palmecology,
Volume 1, Ecology; Mem. Geol. Soc. Amer. 67, p. 609-632, 9 pls., 2 text-figs.
Yonge, C. M., 1940, The biology of reef-building corals, in The Great Barrler expedi-
tion 1928-1929, Scientific Reports; London, British Mus. Nat. Hist., v. 1, no. 14,
p. 353-391.
Manuscript received November 15, 1966

Veracruz, h~lesico
.I. Keith lZighy and William G. Mrlntire
I'nrtable sand Coelmunxty
Awnrinb( i) Communsry
7hu1ai,ia-Hiiiinre*da Cnrna~u~~~ty
?'hrlaiiiir.Porr~ei Cinnmun8ty
Th~l,r,i,~-i)zplori~ Community
f,riiiethan?wr~,,2 gravel C

Some .Octocorallia of Isla de Lobos,
Veracruz, Mexico
~~s~R~c~.--Eunlcea (Eunireopsir) rlauigera Bayer, E. (E.) ralyculara (Ellis & Solander)
forma roronara Bayer, Murirea atlanrira (Kiikenthal), Plexaura honzornalla (Esper),
P. flexuora Lamouroux, P/exaurella dirhotoma (Esper) and Pseudoplero~orgia arerosa
(Pallas) were collected from the lsla de Labos reef, Veracruz, Mexico, during a study
made in August, 1965, by the Coastal Studies Institute of Louisiana State University.
Size, color, zonation, and shape of spiculation is diagnostic; in addition, size, color, and
shape of the colonies is equally important.
TEXT
Page
Introduction and Acknowledgments .... 47
Systematic Zoology .............................. 49
Plexauridae ...................................... 49
Eunirea ......................................... 49
Muricea ........................................ 50
Plexaura ........................................
PIexaurella ....................................
5 1
5 2
Gorgoniidae ...................................... 52
P.reudopferogor.+ ........................ 52
CONTENTS
References Cited ................................ 53
ILLUSTRATIONS
Plates Page
1. Alcyonarians of Isla de
Lobos ................ following page 48
2. Alcyonarians of Isla de
Lobos ................ following page 48
Text-figure
1. Index map ................................ 48
INTRODUCTION AND ACKNOWLEDGMENTS
lsla de Labcrs is located in the western portion of the Gulf of Mexico about
65 miles southwest of Tampico, Tamaulipas, about 35 miles north-northeast of
Tuxpan, Veracruz, and about 8 mlla south-southeast of Cab Rojo, latitude
atrout 21" 27' N and longitude about 97" 14' W (See locality map, Text-fig.
I
-1
Material on hand represents part of the inventebrate collection made during
a five week biologic and sediment study of the reef. Isla de Lobos was selected
for this study by the Coastal Studies InsQiitute at Louisiana State University, Baton
Rouge, Louisiana, because it is the most northern reef in bhe wstern portion
of the Gulf of Mexico which has a sand cay.
Alrhough Octocorallia occur at depths from 75 feet to the reef crest, and
7 species are known, t'hey make up a ainor portion of the invertebrate ppula-
bion on the island.
Dr. Wilkiam G. McInbire originated the study and thanks are accorded him
for his assistance as project administrator. Thanks are also expressed to Dr.
J. Ka~rh Rigby for d ing it plble for bhe writer to participate in borh fidd
and laboratory investigations related to the project. The study is a by-product
of research of the Coastal Studies Institute, Louisiana State University, under
sponsorship of the Geography Branch of the Office of Naval Research, Con-
tract Nonr 1575 (03) NR 388 002.

48 C. KENT CHAMBERLAIN
TEXT-FIGURE 1.-Index map. The reef associated with Isla de Lobos was the major area
of investigat~on, but reconnaissance observations were also made on the associated
Rlanquilla and Medio reefs.
ALCYONARIANS OF ISLA DE LOBOS
FIGS. I-5.-Plexaura flexuosa Lamouroux, 1821. 1. partial colony. 2. enlargement of
branch showing calycae with retracted anthocodia, x3.5. 3. club of outer layer
x107. 4. rod and radiate of inner layer, x92. 5. ovoid and spindmle of middle layer,
x14.
FIGS. 6-9.-Plexaurella dichotoma (Esper), 1791. 6. partial branches. 7. enlargement of
branch showing calycae and dimorphism of zooids, x3.5. 8. quadriradiate of outer
layer, x46. 9. quadriradiate with complex warts from middle and inner layer, x46.
FIGS. 10-16.-Muricea atlantica (Kiikenthal), 1919. 10. large spindle of outer and
middle layer, x14. 11. spined spindle of anthocodial neck, x46. 12. complete
colony. 13-14. rods of inner layer of spiculation, x92. 15. enlargement of branch
showing long, spiny calycae and anthocodia, x3.5. 16. opercular spindles, x107.
FIGS. 17-2 1 .-Eunicea (Euniceopsis) calyculara (Ellsis & Solander), 1786, forma coronafa
Bayer, 1961. 17. colonial view. 18. enlargement of single branch, x3.5. 19. ir-
regular rods and spindles of inner layer, x92. 20. spindle of middle layer, x14. 21.
clubs of outer layer, x107.

CHAMBERLAIN PLATE 1
ALCYONARIANS OF ISLA DE LOBOS

PLATE 2 CHAMBERLAIN
ALCYONARIANS OF ISLA DE LOROS

ISLA DE LOBOS ALCYONARIANS
SYSTEMATIC ZOOLOGY
Fam~ly PLEXAURIDAE Gray, 1859
Genus EUNICEA Lamouroux, 1816
Kevzark~.-See Bayer (1955, 1956, 1961) and Deichmann (1936) for a definition of the
genus and keys to the speues.
EUNICEA (EUNZCEOPSIS) CLAVIGERA Bayer, 1961
Plate 2, figs. 12 to 19
?Eunirea furgrda Ehrenberg, 1834, p. 364.
?Plexaura turgzda Verrrll, 1864, p. 35.
Eunrrea (Eunireopsi~) rlavigera Bayer, 1961, p. 147.
Desrnpiron.-A few branches only of Eunicea (Eunzreopsis) rlacigera Bayer were collected.
Longest branch 21 cm. long and 7 mm. wide, branchlets 3 mm. wide, propottionally
long' and slender. Colony shows lateral branching; seldom, if ever, dichotomous.
Colony as a whole is bushy, branching roughly In the same plane. Dry color light yellowbrown.
Numerous zooids, randomly disposed over the branches and branchlets. In a state
of dry preservation, zooids are raised on the lower lip.
Chestnut brown gorgonian core has soft, chambered axis strung irregularly through
center Cortex made of gorgonian laid down in tight, concentric layers.
There are three distinct layers of spiculahon. Innermost layer forms a sheath of
small purple sclerites around core. These are mostly thick spindles displaying numerous
compcund tubercules but also slender spindles displaying sparse conical projections and
occas~onally small capstans, rods and radials. Size ranges from 0.08 to 0.30 mm. Middle
layer mostly occupied by large spindles which are toxoid, sigmoid, arcuate or straight;
they are colorless w~th an occasional purple hue or purple core. Length ranges up to 3.4
nim , and averages between 2 to 3 mm., 4.5 to 8.4 times as long as wide. Sclerites adjacent
to purple sheath frequently pale purple, nat always simple spindles, but may be compound
spindles and double clubs. Outer layer of spiculation composed of colorless
foliate and wart clubs ranglng from 0.1 to 0.26 mm., but averaging about 0.18 mm. in
length. Opercular sclerites are small irregular rods, 0.06 to 0.20 mm. in length.
Remarks.-Four branches were collected south of the reef crest (field locality #38) at
a depth of 60'. This is close to the base of the reef and is a zone essentially of Montasfrea
(Scleractinian) with intervening sand aprons.
The material on hand varies from the three specimens described by Bayer (1961) in
that the clubs at the outer layer are double the size given by him.
ALCYONARIANS OF ISLA DE LOBOS
FIGS. 1-5.-Pseudopterogorgra arerosa (Pallas), 1766. 1. single pinnate branch. 2. enlarge-
ment of pinnules, x3.5. 3. scaphoid of outer layer, x107. 4. colorless spindle of
inner layer, x107. 5. violet spindle of inner layer, x107.
FIGS. 6-11.-Plexaura hornomalla (Esper), 1792. 6. enlargement of branch, x3.5. 7.
partial colony. 8. spindle of m~ddle layer, x14. 9. rad~ate and spindle-rod of inner
layer, x92. 10-11. clubs of outer layer, x107.
FIGS. 12-19.-Eutzicea (Eunireopsis) rlavigera Bayer, 1961. 12. club of outer layer, x107.
13. complex "warts" of large spindles, x214. 14. opercular rod, x214. 15. micm
scleres, relation undetermined (common to several of the species on hand), x214.
16. patt~al colony. 17. enlargemeM of branch, x3.5. 18. spindle of middle layer,
x14. 19. rods, and spindles of imer layer, x92.

50 C. KENT CHAMBERLAIN
EUNICEA (EUNICEOPSIS) CALYCULATA (Ellis & Solander),
1786, forma CORONATA Bayer, 1961
Plate 1, figs. 17 to 21
Eunicea (Eunrreopsis) calyculda (Ellis and Solander), 1786, forma coronda Bayer, 1961,
p. 158.
Desrrrption.-Glon~es 10-18 cm. high. Main stem short or nonexistent, major branches
begin almost immediately and show lateral branching with branchlets, usually, but not
always, located all on same side of branch. Branches about 7 mm. and branchlets about
4 mm. in diameter. Medium to dark brown, almost black.
Verrucae highest on lower side. Infolded anthocodia occasionally visible from
exterior.
Inner layer of coenenchyme tight, concentric layers of chestnut brown gorgonian
with a soft, chambered axis. Colorless or pale violet spindles and rods with some
radiates and clubs form a sheath about the core; range from 0.08 to 0.24 mm. in
length. Arranged w~thin organic sheath as rows of sclerites running parallel to axis.
M~ddle layer of spiculatlon of colorless slender sp~ndles with a few clubs and fat
spindles, range from 1.4 to 2.0 mm. long, 3.5 to 6.1 times longer than wide. Spicules
adjacent to violet sheath often pale violet and small. Outer layer contams small wart
clubs 0.09 to 0.14 mm. long. Opercular sclerites slender rods or clubs with small,
irregular, knobby warts, range from 0.05 to 0.17 mm. long.
Remarks.-Several colonies were collected from 60 feet deep, in an area composed
principally of Montastrea with Intervening sand aprons.
Genus MURICEA Larnouroux, 182 1
Remarks.-See Deichmann (1936)' and Bayer (1961) for a definition of the genus
and keys to the specles.
MURICEA ATLANTlCA (Kiikenthal), 1919
Plate 1, figs. 10 to 16
Gorgonla muricata Lamarck, 1815, p. 163; not Gorgonia murrcata Pallas, 1766, p. 198.
Murrcea murrcata Verrill, 1907, p. 301. f~gs. 144-145, pl. 33B, fig. 2a, pl. 33C, f~g. 2d,
pl. 36, fig. 2(7); Deichmann, 1936, p. 100, pl. 6, f~g. 1, pl. 9, figs. 1-3, Stiasny,
1941a, p. 262, figs. 9-10; Aurivillius, 1931, p. 105, fig. 20.
Eumuricea atlantica Kiikenthal, 1919, p. 907; Ries, 1929, p. 399, pl. 8, fig. 4.
Eun~rensis dentata Dubrowsky, 1934, p. 11, figs. 11-15, 21-22, 24-48; pl. 1.
Murired atlantira Bayer, 1961, p. 184, fig. 56, pl. 5, fig. 4.
Descrrptron.-Slngle colony collected, now dry, is 20 cm. high and 10 cm. wide. Present
dry and or~ginal wet color white to straw yellow. Some branches, broken from another
colony, are 22 cm. long. Main stem of complete colony splits almost immed~ately above
base Into two horizontal branches about 6 cm. long which give rlse to abut six vertical
branches. Vertical branches have 3 to 4 lateral or d~chotomous branches; some fusion
occurs at convergences Branches 1 cm w~de, branchlets 5 mm. w~de. Branches and
branchlets show a slight tendency to remaln in same plane, but colony has bushy nature
Verrucae numerous, crowded over root area, stem, branches and branchlets. Verrucae
remaln extended, about 3 mm. long, inclined upward.
Core soft chambered and unjointed axis surrounded by loculated, chestnut brown
and concentric-layered gorgonia, flattened in same general plane of branching.
Spiculat~on in three layers as in Eunirea though such zonation not quite as dlstinct~ve.
Inner layer or sheath adjacent to core made up of small spindles, ovoids, and
octaradiate capstans, 0.12 to 0.54 mm. long. iMiddle layer made of small, slender
spindles whlch bear only a moderation of s~mple conical projections. Large spindles,
less than 2.0 mm. long, make up base of lower 11p of calyces; similar spindles continue
en echelon out to crown, becoming smaller and more spinose on outside, and develop-
Ing term~nal spines, part~cularly on the near crown spindles. On the ~ns~de they are
covered w~th complex warts. Upper lip of calyces pr~ncipally a flexible tissue wall,
but bear slender spindles about 0.4 mm. long and moderately covered with conical
projections. Opercular scler~tes small spindles or scaphoids, 0.1 to 0.3 mm. long and
covered with cuspate processes. All spicules colorless.

ISLA DE LOBOS ALCYONARIANS 5 1
Remarks.-This specles was collected on the southwest side of Isla de Lobos m 10-15
feet of water. Thls 1s field locality #43 and is about 100 feet from the reef crest
In an area predominantly of dead Diplorra and Monrartveu covered with a mat of
brown and green algae.
Genus PLEXAURA Lamouroux, 1812
Remarkr.-See Bayer (1961) for a definition and key to the genus.
PLEXAURA HOMOMALLA (Esper), 1792
Plate 2, figs 6 to 11
? Gorgonia humosa Esper, 1791, v. 2, p. 36, pl 6.
Gorgon~a homomalla Esper, 1792, p. 104, pl. 29.
Plexuu,a homomalla Verr~ll, 1907, p. 304, fig. 147, pl. 35A, flg. 3; Kiikenthal, 1924, p.
117; St~asny. 1935a, p. 66; Bayer, 1956, p. F210; Bayer, 1961. p. 95.
Plexauropsis tricolor Stiasny, 1935b , p. 69, fig. R, pl. 3, flg. 12.
Plexaura flexuora Stiasny, 1941b, p 105.
Desrrrption.-Some variety exists in the external appearance of two specimens on hand
identified as Plexau~a homonzalla (Esper). Branch from west side of lsla de Lobos is
26 cm long, and termlnal branches are 4 mm. In diameter, proportionally long and
slender. Branch from Arrec~fe Blanquilla 1s 6 cm. long, and terminal branches are 2.5
mm. wlde. Branchlets are all on one slde of main branch rlsing vertically and zoolds
absent on lower side. Verrucae numerous with ra~sed lower lip tiltlng upward.
Central core composed of concentric layers of gorgonia with a soft, chambered
Irregular center. Inner sheath composed of stubby violet capstans, splndles and radials.
0 05 to 0.24 mm. long. Scler~tes of mlddle layer colorless, violet cored, or v~olet
splndles, less than 2.0 mm. In length and 3.0 to 6 5 t~rnes as long as wide, curved,
toxoid or stra~ght Outer layer of spiculat~on made of foliate clubs and unilateral
sp~ndles, colorless and 0 14 to 0.58 mm long. Anthocodla1 sclerites Irregular rods and
sp~ndles 0.09 to 0.26 mm. long, acutely slender.
Rernarbr.-The partral colony from lsla de Lobos was collected from 10-15 feet of
water In the lee reef, about 100 feet from the west reef crest (field station #42). This
1s a region mostly covered with an algae mat on dead coral. The smaller specimen collected
from Arrecife Blanquilla had apparently been washed about the tidal flat ~udging
from the worn condition of the specimen.
PLEXAURA FLEXUOSA Lamouroux, 1821
Plate 1, figs. 1 to 5
Plexaura flexuosa Lamouroux, 1821, p. 135, p. 70, figs. 1-2; Gordon, 1925, p. 19, pl. 4,
f~g. 4a-c; Stlasny, 1935b, p. 57, pl. 4, fig. 18, pl. 7, figs. 35-36; Bayer, 1961, p. 104,
flg. 23, pl. 4, f~g. 4, pl. 16-17, not P1exaur.a flexuos~ Stiasny, 1941b, p. 105.
Plexaura flexuosula Kukenthal, 1924, p. 118.
Plexaura salicordnoides Milne, Edwards and Haimes, 1857, I, p. 153, pl. B2, fig. 2.
Plexaura murica Duchassaing and Michelotti, 1860, p. 28, p. 3, figs. 9-10; Gordon, 1925,
p. 17, pl. 3, figs. 1, 8, pl. 4, fig. 1.
Plexaura edu~ardsr St~asny, 1935, p. 51, fig. 10, pl. 4, figs. 19-20, pl. 7, fig. 34.
Eunrrella marquesarum Kiikenthal, 1919, p. 906, Stiasny, 1938, p. 27, pl. 3, figs. 9-10;
pl. 8, f~gs. 30, 33.
Eunirea humilrs Stiasny, 1935b, p. 74, fig. T; pl. 3, fig. 14; pl. 7, fig. 32.
Eunrrea hicksonr Stiasny, 1935a, p. 115.
Descripiron.-Spec~men, identified as Plexaura flexuosa Lamouroux, is ody a partial
colony. Yellow branch in dry state. Main branch 7 cm long and 6 mm. wide, and cons~dered
to have lain horizontally near the bottom since branchlets are all on one side,
perpendicular to branch, and lower s~de is void of zoolds. Longest branchlet 4 cm long
and 6 cm. wide, branching dichotomously and sometimes laterally.
Verrucae prominent, numerous and seemingly randomly arranged. Eight points of
the anthocodiae easily visible on exterior, only sli htly recessed below rim.
Gorgonian core has the usual soft, chamfered axis while gorgonian itself is
the usual chestnut brown in tight, concentric layers.

5 2 C. KENT CHAMBERLAIN
Inner layer of spiculation purple sheath of short, squatty spindles and rods, 0.05
to 0.20 mm. long Middle layer of spiculat~on shows gradation in color as well as in
form of sclentes; from Inward out, deep purple to colorless, and large scler~tes slgmold,
toxold, arcuate or stralght spindles, maxlmum size noted 1.85 mm., ovoids, radiates and
clubs nearly as large. Smaller spindles, radlals, ovoids and clubs occur as well, average
length 0.9 mm. Forms of the sclerltes show no preference in color, but are randomly
mixed and colorless, violet hued or deep violet. Outer layer composed exclusively of
colorless leaf clubs, 0.14 to 0.19 mm. long. Sclerites of anthocodial polnts slender, irregular
sp~ndles and rods, 0 09 to 0.22 mm. long.
RemarRr.-Th~s specimen was collected as a loose sample ~n the littoral zone of the northwest
port~on of the reef in 2 to 4 feet of water on the leeside of the tidal flat (traverse
#5).
Genus PLEXAURELLA Kolliker, 1865
Revz~rkr-See Bayer (1956, 1961) for summary of the genus and a key to the species.
PLEXAURELLA DICHOTOMA (Esper), 1791
Plate 1, figs. 6 to 9
Gorgonra Lrhotonza Esper, 1791, p. 59, pl. 14.
Euniretr anreps Duchassang and Mlchelotti, 1860, p. 25, pl. 3, figs. 1-2.
Plexaul.ella dichototna Hargitt and Rogers, 1901, p. 285; Vernll, 1907, p. 310, figs 156-
157, pl. 33B, flg. lb, pl. 36A, fig. 2, pl. 36A, flg. 1; Kunze, 1916, p. 569, flgs
N-P, pl. 28, 61g. 5, Bayer, 1956, p. F212; Bayer, 1961, p. 170, fig. 50, pl. 6, flgs.
6-7, PI. 23, 24, 25.
Plexaurella c~irndrica Verr~ll, 1912, p 384, pl. 32, fig. 7, pl. 34, fig. 4, pl. 35, f~gs. 4, 14
Plexaurella brazrlrnna Vetrill, 1912, p. 385, pl 34, flgs. 3-3a, pl. 35, flgs 12-12a, 15
Plexaur'ella obesa Verrrll, 1912, p. 383, pl. 31, flg. 3, pl. 32, flg. 9; pl. 34, fig. 6.
Plexaurella heteropora Kunze, 1916, p. 567, flgs K-M, pl. 27, fig. 4
Plexaurella rurrata Kunze, 1916, p. 582, figs B'-E', pl. 27, flg. 9.
Description.-Plexaurella much like saguaro cactus in appearance with thick stalk and
lateral branches. Branches on hand 8 to 12 cm. long and 1 to 1.4 cm. wlde Verrucae
small rlms about zooid, numerous and randomly arranged. In present dry, and perhaps
~n origlnal wet condition, apertures are narrow sl~ts 0.8 to 1.2 mm. long. Several small
clrcular zoolds probably represent d,lmorphlsm (see Plate 1, fig 7). Colony pale brown
when dry.
Central cortex composed of gorgonia with a soft, chambered, irregular axis Gorgonia
portion mostly composed of lenticular calcite rods wlth thln gorgonla layers separating
them. In cross section, SIX canals vlslble running parallel and adjacent to axls, smaller
canals run through splculated coenenchyme connecting zooids
Sp~culation 1s rather un~form w~th colorless quadrlradiates predom~nating, but
with some spindles, tr~radlates, and sexradiate capstans. Slze varies from less than 0.20
to 0.47 mm. Anthocoidal rods are approximately 0.06 mm. long
Remarks.-Branches of Plexautella drrhotoma were collected from 10 to 15 feet deep
on the lee of Isla de Lobos, about 100 feet from the seaward slde of the red crest
(f~eld locality #42) as well as from the south s~de on the windward edge.
Famlly GORGONIIDAE Lamouroux, 18 12
Genus PSEUDOPTEROGORGIA Kukenthal, 1919
Remarks.-See Bayer (1961) for a definlt~on of the genus and a key to the species.
PSEUDOPTEROGORGIA ACEROSA (Pallas), 1766
Plate 2, figs. 1 to 5
Gorgonra arerosa Pallas, 1776, p 172, Esper, 1792, v. 2, p. 106, pl. 31.
Gorgonia setosa Esper, 1791, v. 2, p. 66, pl. 17.
Plerogorgia pinn~ta Milne-Edwards and Haime, 1857, v I, p 168, not Gorgonra pznnata
Linnaeus, 1758, p. 802.

ISLA DE LOBOS ALCYONARIANS 5 3
Pterogorgia biprnnata B~elschowsky, 1929, p. 213, fig. 37, pl. 4, fig. 21, not Pterogorgia
hrprnnata Verr~ll, 1864, p 31.
Pterogorgra arerosa, forma typrca and forma avbusrula B~elschowsky, 1929, p. 209, figs.
12-34, pl. 4, figs. 18-20, not Pterogorgia arerosa, var. elastira Bielschowsky, 1929,
p. 210, flg. 35, pl. 5, fig. 23, not Pterogorgia arevosa, var. rr~ida Bielschowsky,
1929, p. 212, fig. 36, pl. 5, fig. 24.
Pterogorgra arevosa Delchmann, 1936, p. 198, pl. 21, figs. 17-20.
Pterogorg~a ellr.rrana Deichmann, 1936, p. 199, pl. 21, figs 21-24, not Pterogorgta
ellr.nuna Milne-Edwards and Haime, 1857, v. 1, p. 169.
Pterogorgra arerosa, var. elasfrra, Stiasny, 1941b, p 112.
Antrllogorg~a arerosa Bayer, 1951, p. 91-102; Bayer. 1956, p. F212.
Pteudopterogorgia arerosa Bayer, 1961, p. 240, flg. 76, pl. 9, fig. 3.
Desrrrptjon.-Colony somewhat bushy, about 1.3 mm. high and 1 mm. wide, stands
erect, and colored wh~te, pale yellow-brown or pale violet. Two main stems and
numerous branches, heavily pinnate. Single branch collected 1s 28 cm. long; pinnules
range from 12 cm. near stem to 3 cm. at tip of branch. Branches and pinnules generally,
but not strictly, arranged ln same plane Both branches and plnnules round in cross
sectlon but may tend to be compressed ~n plane of alignment
Zooids not observed on stems, but where present on branches, they are on upper
surface toward stem and form small clusters. Zooids arranged en echelon or in parallel
rows on lateral edges of plnnules, occasionally cross from one edge to the other.
Branches about 7 mm. at thickest parts and pinnules 3 mm. Plnnules occasionally show
dichotomous branching.
Central chord soft, chambered and unjolnted thread 0.04 mm. in d~ameter, sur-
rounded by concentric layers of red-brown, horny gorgonia wh~ch makes up about a
quarter of the d~ameter of a pinnule. Some lenticular layers of calcite occas~onally in-
cluded w~thln gorgonla layer. Zooids imbedded in coenenchyme wlthout verrucae.
Spiculation consists of two layers Outer layer made of colorless scaphoids, spindles
and rods while Inner layer made of colorless and violet spindles or rods Scaphoids
smooth on convex side with 4 to 8 sets of processes on concave side. Size ranges from
0.14 to 0.18 mm. in length. Most sp~ndles are smooth in the middle with four sets of
warts clustered on each end. Anthocodial sclerites small irregular rods, 0.06 to 0.10
mm. long.
Remarks.-Collected from the southwest side (leeside, field station #43) of Isla de
Lobos in 10 to 15 feet of water and about 100 feet seaward from the reef crest. In
general, the area consists of dead Drploria and Monta.rtiea covered with a mat of brown
and green algae.
This species is common throughout the greater part of the western Atlantic
REFERENCES CITED
Aurivillius, M., 1931, The Gorgonians from Dr. Sixten Bock's Expedition to Japan
and Bonin Islands, 1914; Kungl. Svenska Vetensk. Akad. Handl., Ser 3, v. 9, no. 4,
p 1-337, 6 pls., 65 text-flgs.
Bayer, F. M., 1951, A revision of the nomenclature of the Gorgoniidae (Coelenterata:
Octocorallia), with an illustrated key to the genera; Jour. Wash. Acad. Sci., v. 41,
no. 3, p. 91-102, 3 figs.
---- , 1955, Contributions to the nomenclature systematics and morphology of the
Octocorallia; Proc. U. S. Nat. Mus., v. 105, p. 207-220, pls. 1-8.
---- , 1956, Octocorall~a, in Moore, R. C. el al., Treatise of invertebrate paleomtology,
Part F, Coelenterata; Geol. Soc. Amer. and Univ. Kansas Press, p. F166-F231, figs.
134-162.
---- , 1961, Studies on the fauna of Curacae and other Carribbean Islands: No. 55.
The Shallow-water octocorallia of West Indian Region; Natuurvet Stud. Surimane,
v. 12, no. 23, 373 p., 27 pls., 101 text-figs.
Bielschowsky, E., 1929, Die Gorgonarlen Westindiens. Kap. 6, Die Familie Gorgoniidae
zugleich eine Revis~on; Zool. Jahrb., Supplement 16, Heft 1, p. 63-234,
pls. 2-5, 40 text-figs.
De~chmann, E., 1936, The Algonaria of the western part of the Atlantic Ocean;
Mon. Mus. Comp. Zool. Harvard, v. 53, 317 p., 37 pls.

54 C. KENT CHAMBERLAIN
Dubrowsky, S., 1934, Studien uber Westindische Gorgonarien; Natationes Biologicae.
Bucuresti, v. 2, no. 1, p. 1-1 5, 3 figs.
Duchassaing, de F. P. and Michelotti, H., 1860, MPmoire sur les Coralliaires des
Antilles; Mem. Roy. Acad. Sci. Torino, set. 2, v. 19, p. 279-365, pls. 1-10.
Ehrenberg, C. G., 1834, Die Corallenthriere des Rothen Meeres physiologisch untersucht
and systematisch verzeichnet; K. Acad. Wissensch. Abh., Berlin, 1833-1834,
11. 1-152.
Ellis. J., and Solander, D., 1786, The Natural History of many curious and uncommon
Zocn~hytes collected from various parts of the globe; p. i-xii, 1-208, pls. 1-63, London.
Esper, E. J. C., 1791, Die Planzenthiere in Abbildungen nach der Nature mit Farben
erleuchtet nebst Beschreibunden; Niirnberg, v. 2, p. 1-96; 1792, v. 2, p. 97-180.
Gordon, I.. 1925, Gorgonaids from Curacao Island; Het Koninklijk Zool. Genotschab
Leyden, Bijddrag tot de Dierkunde, 24 Aflevering, p. 15-24, pls. 3-4.
Hargitt, C. W., and Rogers, C. G., 1901, The Alcyonaria of Porto Rico; Bull. U.S.
Fish Commission, v. 20, pt. 2, p. 265-287, 4 pls.
Kolliker, R. A,, 1865, Die Bindesubstanz der Coelenteraten; Icones hist. oder Atlas der
vergleich. Gewebelehre, v. 2, Leipzig, p. 87-181, figs. 16-28, A, B, pls. 10-19.
Kukenthal, W., 1919, Gorgonaria; Wissmsch. Ergebnisse der deutschen Tiefsee-
Expedition auf dem Dampfer Valdivia, 1898-99; v. 13, no. 2, p. 1-946, 138 figs.,
pls. 30-89.
---- , 1924, Gelenterata, Gorgonaria; Das Tierreich, v. 4, p. i-xxviii, 1-478, 209 figs.
Kunze, G., 1916, Die Gorgonarien Westindiens. Kap. 425, die Gattung Eunicea, die
Gattung Plexaul-ella; 2601. Jahrb., Suppl. 11, pt. 4, p. 505-586, pls. 24-28.
Lamarck, J. B., 1815, Suite des polypiers corticifkres; Mem. Mus. Nat. Hist. Nat. Paris,
v. 2, p. 74-84, 157-164, 227-240.
Lamouroux, J. F. V., 1812, Sur la classification des Polypiers coralligenes non entiCrement
pierreux: Nov. Bull. Sci. Soc. Philom., v. 3, p. 161-188.
---- , 1816, Histories des polypiers coralligenes flexibles, vulgairernent nomines
zoophytes; p. i-xxiv. 1-560, pls. 1-19.
---- , 1821, Exposition methodique des genres de I'Ordre des Polypiers; p. i-viii,
1-115, 184 pls.
Linnaeus, C., 1758, Systema naturae per regna tria naturae. . . Edition 10, reformata.
(Holmiae) Stockholm.
Milne-Edwards, H., and Haime, J., 1857, Historire naturelle des coralliaires ou
polypes proprement dits; 3 v., p. i-xxxiv, 1-326, 1-633, 1-560, atlas of 36 pls.,
Paris.
Pallas, P. S., 1766, Elenchus zoophytorum sistens generum adumbrationes generaliores
et specierum cognitarum succinctas descriptiones cum selectis auctorum synonymis; p.
i-xvi, 1-45 1, ~Gae-corniturn.
Riess, M., 1929, West Indian Muriceidae; Zool. Jahrb., Abt. Syst., Suppl. 16 Heft 2,
p. 377-420, pl. 8, 4 text-figs.
Stiasny, G., 1935a, Uber Plexauropsis humilis (Milne-Edw.) und Unicea hicksoni nov.
spec. (Gorgonaria, Plexauridae); Zool. Anz. 112, p. 107-116, 3 figs.
---- , 1935b, Die Gorgonacea der Siboga-Expedition. Supplement I. Revision der
Plexauridae; Siboga Exped. Monogr. 13b7, 106 p., 27 figs., 7 pls.
---- , 1938, Revision des Plexauriden Genus Eu~zicella Verrill (Versuch einer Synthese);
Kon. Ned. Akad. Wet., Verh., 2nd ser., v. 37, p. 1-37, 8 pls.
---- 1941b, Gorgonaria von Venzuela (Inseln Blanquilla und 10s Frailes); Arch.
~ierl. Zool., v. 6, p. 101-116, 4 figs., 2 pls.
Verrill, A. E., 1864, List of the polyps and corals sent by the Museum of Comp. Zool.
. . . , with annotations; Bull. Mus. Comp. Zool., vol. 1, p. 29-60.
---- , 1907, The Bermuda Islands, pt. 5; Trans. Conn. Acad. Arts & Sci., New
Haven, v. 12, Art. 2, p. 45-418, 41 pls.
---- , 1912, The Gorgonians of the Brazilian Coast; Jour. Acad. Nat. Sci. Philadelphia,
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Manuscript received May 24, 1966

Dinosaur Eggs from the Upper Cretaceous North Horn
Formation of Central Utah
ABSTRACT.-The discovery of fossil egg materials in the Upper Cretaceous North Horn
Formation in the Wasatch Plateau of central Utah includes the first fossil eggs found
in the western hemisphere which may be attributed to dinosaurs. Previous discoveries
of a few scattered fragments in various regions have not provided enough material for a
significant study of Mesozoic reptilian eggs.
Preliminary studies show this new material represents, from one area, various types
of eggs described from widely separated regions of the world. It may now be possible
to establish a more realistic distinction between the fossil eggs of reptiles and birds than
has been done in the past. Some of the shell fragments bear an ~nteresting resemblance
to those belonging to certain fossil birds and may have a bearing on studies of problems
involved in the origin of birds from their reptilian ancestry.
This material represents the greatest variety of fossil egg materials, although not
the greatest volume, to be found in sediments of the Mesozoic Era. Three broad classes
of egg types can be recognizd on the basis of their external appearance. These have
been designated as Clas~ A, eggshells with a smooth exterior surface, Class B, those with
a nodose or nodular surface and Cla.rs C, fragments having a sculptured exterior surface.
CONTENTS
TEXT
page
Discussion ...........................................
References Cited ..................................
63
67
Introduction .......................................... 55
Acknowledgments ............................
Occurrence .........................................
Description ...........................................
57
57
59
ILLUSTRATIONS
Text-figures
1. Index map of dinosaur
Page
Class A .......................................... 60
External appearance .................... 60
Pores ........................................ 61
egg locality ................................ 56
2. Generalized stratigraphic
section of egg locality ............ 58
Internal appearance ......................
Discussion ....................................
61
62
Plates
1. Individual eggs and weathered
Class B ........................................ 62 cross section .... following page 64
External appearance .................... 62
Pores .......................................... 62
2. Exterior shell structures
.......................... following page 64
Internal appearance .................... 62 3. Exterior-Interior views of
Class C ............................................ 63
External appearance .................... 63
Pores ........................................ 63
Internal appearance ...................... 63
4.
three fragments
.......................... following page 64
Radial and tangential
cross sections .... following page 64
INTRODUCTION
Dinosaur skeletons have been found on every continent and subcontinent,
and yet discoveries of dinosaur eggs, if in fact they did all lay eggs, are quite rare.
Recent discoveries of numerous fossil reptilian eggs in South China (Qzumg-
Chein, 1965), together wih earlier discoveries in Mongolia (V. van Straelen,
1925), and in various localities in France (Thaler, 1965), have provided in-
vestigators with most of the material studied in the Fast. An empirical study
by Chung-Chien (1965) of the excellent material from South China does not
include studies of the shell microstructure, so it is not possible, at this time, to
make any detailed comparisons of that material with the Mongolian or French
eggs.

JAMES A. JENSEN
TEXT-FIGURE 1.-Index map of dinosaur egg locality.
The search for fossil Mesozoic eggs in the western hemisphere has not
been carried out in a systematic fashion, but rather, discoveries have been the
fortunate result of other collecting. Egg fragments are known from very few
discoveries such as those of Brazil (Thaler, 1965), Montana (Jepsen, 1931),
and Utah (Gazin, 1964, personal communication). These localities of chance
discovery have simply told us egg-laying reptiles were present and very little
else.
The first relatively complete dinosaur eggs to be found in the western
hemisphere were collected by the author in July, 1966, from the Upper Cre-
taceous North Horn Formation in the Wasatch Plateau of Central Utah. (Text-
figs. I, 2). Later in the same season additional fossil egg materials were col-
lected from the same area by Mr. Donald Busge d the College of Eastern Utah.
This material will be figured in a future study by the author.
The vertebrate fauna of bhe North Horn Formation was reviewed by C. W.
Gilmore (1946) as a result of discovery of vertebrate remains in that forma-
tion by E. M. Spieker in 1934. Spieker again visited the area in 1935 and

CRETACEOUS DINOSAUR EGGS 57
collected materials pertaining to hadrosaurian and ceratopsian dinosaurs. He
subsequently differentiated the North Horn Formation largely on the basis of
these Upper Cretaceous fossils in its lower member.
- -
The Smithsonian Institution sent an expedition to investigate the region in
1937 under the direction of C. W. Gilmore. Subsequent expeditions were
carried out in the years 1938, 1939, and 1940, under the direction of C. L.
Gauin, also of the Smithsonilan In~ti~tut~ion. These field parties collected skeletal
materials from five different reptilian orders, although none of the individual
skeletal remains, except the saurians, were very complete. Important ~nformation
was obtained, however, regarding the distribution and variety of Upper
Cretaceous vertebrates in Utah, as noted by Gilmore (1916) in his review of
the known fauna of the formation.
Acknowledgments
The author wishes to express appreciation to various lndiv~duals who have
extended assistance in the preparation of the manuscript and materials, -with
special appreciation being extended to Dr. J. Keith Rigby of the geology staff
for his enthusiastic encouragement of the project and for his talented and
patient assistance ln all of the physical as well as the technical problems encountered
by the author. Thanks is also expressed to Dr. Morris S. Petersen
for X-ray diffraction tests made of shell specimens and for his assistance in
collecting additional materials for study. Affectionate appreciation is expressed
to Marie M. Jensen for extensive revisionary efforts at the typewriter. Recogn'ition
must be made of the value of the amateurs' role i,n exploratory f,ield work
as demonstrated by Mr. Louis Jones, who assisted in the discovery of the firs,t
c~mplete eggs, and Mr. Carlyle Jones, whose growing knowledge of the regions
surrounding hmis home and his helpful cooperation as well have been imprhnt
factors in making this paper poss~ble.
- - -
The materials were collected from the Manti-LaSal National Forest under
the authori.ty of bhe Antiquitties Aot of 1906 by a permit issued for the calendar
year of 1966 to the Geology Department of the Brigham Young University at
Provo, Utah.
OCCURRENCE
In his review Gilmore (1946) notes that all of the vertebrates collected
by the Smithsonian expeditions occured in the lower 850 feet of the North
Horn Formation, dhich consists of variegated shales and sandstones which are
conglomeratic in places. The egg materials collected by the author in July,
1966, were in these same beds, (Text-fig. 2) with the most complete eggs
occurring approximately ten feet above the horizon where a partial skeleton
of a large sauropod, Alamosaurus sanjuanensis, was collected by Gilmore in
-
1937.
The vertebrate faunal assemblage of the North Horn Formation will be of
pointed interest in following studies since it is assumed that the variety of
reptiles present in that region during the Upper Cretaceous was equal, at least
in number, to the different species represented by the various eggs and shell
fragments collected. This paper will not attempt a reconciliation of the
various eggs with their parents since no means are available for the positive
identification of fossil eggs with the skeletal remains of the animals which
produced them. Mere association of eggs and bones in a sedimentary deposit

58 JAMES A. JENSEN
North Horn
Formation
---
---
Zone Ill shell fragments
~ H O ~ ~ O femur S O U ~
one If shell fragments
-abraded bone fragments
Zone I whole eggs
TEXT-FIGURE
2.-Generalized stratigraphic section of the lower North Horn Formation
at the dinosaur egg locality showing the relationship of the three egg horizons to
other vertebrate fossil occurrences. Vertical scale 1 inch equals 20 feet.

CRETACEOUS DINOSAUR EGGS 59
is incomlus~ve evidence of their family relationship. The only fact available
is that they were buried together. Further, no precise method has yet been
discovered to enable a spfic differentiation between one fossil egg and
another.
The eggshell deposits of Utah are of particular interest because the variety
of animals represented by these remains appears, at this time, to exceed that of
any majar fossil egg locality of bhe world.
Three distinct zones containing fossil eggs or eggshell fragments are
present in the area studied by the author in the North Horn Formation. These
are provisionally designated as Zone I, 11, and 111, beginning at the lowest
occurrence in the section. (Text-fig. 2). Four partially complete eggs, two
crushed and two in reasonably normal ovoid shape, were collected from a very
fine-grained, soft, white sandstone in Zone I. This white sandstone is overlain
by 10 feet of deeply weathered, variegated shale followed by 2 feet of light
tan, friable sandstone. 'Ilhis sandstone is overlain by 15 feet of variegated
shale containing numerous broken and abraded bone fragments in the upper
regions. Identifiable fragmen,ts represent turtles, had'rosaurians, ceratopsians and
possibly other dinosaurs and are accompanied by rare fragments of eggshell.
This shale is overlain by two feet of light tan, friable sandstone which is fol-
lowed by 4 feet of variegated shale containing egg Zone II ~n its upper part.
No joined or related fragments of eggshell were observed in this zone and
although the abundant remains show great variation wlthin one pattern of
sudace ornamenbabion, they may yet pentain to a single species. The fragments
occur in a grey-green, deeply weathered shale, unlike the white sandstone of
Zotzc I, and may be the outwash of hatched eggshells from the "laying
beds" rather than the site of the original nest.
Zone II is overlain by a friable sandstone which interfingers with channel
sandstones to the west and terminates upward in a cliff which forms the top
of a ridge, approximately 38 feet above the zone. From this point one must
offset approximately 200 feet in a northwesterly direction to where the section
continues upward an additional 80 feet to the crest of another ridge.
This portion of the section is also composed of alternating friable sand-
stone and deeply weathered shale with some of the sandstone beds being slightly
conglomeratic. Zone 111 (Text-fig. 2) occurs in a deeply weathered shale at
the top of the ridge. Here the eggshell fragments appear as transported
materials rather than those of an original nesting area since no eggs were
found in situ but only fragmentary remains of variously atterned shells. This
zone is approx~makly 153 feet above Zone I and 165 eet above the lowest
occurrence of shell fragments observed in the area.
DESCRIPTION
In the past when distinct, definable fossil eggs have been found it has
been the custom to give them specific names as a matter of convenience. These
names seldom relate the egg to its parentage since this is not possible unless
embryonic remains are present for study. The names, therefore, are based
largely upon the physical characteristics of the egg itself, localities, or personal
memorials.
No names for the Utah egg materials will be proposed in thls paper but
several preliminary classes of eggs will be established simply upon the basis
P

60 JAMES A. JENSEN
of their external appearance witlh brief reference to thelr microstructure. Future
studies by the author will pursue a positive means for specif~c differentiation,
a goal sought by V. von Nathusius as early as 1868. Modern techn~ques and
Instruments may now provide a more exacting treatment of the problem.
On the same basts of differentlat~on as used by Thaler (1965) in h~s
description of fossil eggs from France, at least ten drfferent species could be
defined from the Utah mater~al. However, slnce the Utah specrmens appear k~
be more dlverse and somewhat different than those d~scussed by Thaler, hls
methods will not be used here, and only broad classes will be distinguished
Dendine further studv.
1 "
Three gross classes of external shell structure are apparent in the North
Horn eggs. We shall deflne them for the present as Class A-Eggs w~th a
smooth exter~or surface; Class B-Eggs wlth a nodose, or nodular surface
wherein the structures are expressed above the c~rcumference of the shell; and
Class C-Eggs w~th a sculptured surface wherein a dlverse pattern of prts,
cones and errat~c channels is developed below bhe clrcumference of the shell
in such a manner that the traverse of an arc around the egg's exterior surface
would not be interrupted by the pattern.
An almost inflnite number of subdivisions are to be found withln these
three classes of shell structure. In areas of extreme simplification of erther
Clas B or C ~t IS diff~cult to separate them from a rough variety of Class A.
Studies of the mrcrostru~ture has then proven necessary to make a dist~nct~on.
Class A
Materials collected which fall into this class by reason of the~r smooth
external surface ekhiblt an interesting variety of internal structures. Some are
remarkably well stratifred w~th as many as twenty vrsable layers whlle others
may be slmply div~ded into two or three peripheral zones differentiated by color
and cleavage. In this latter group the zones appear to coincide with those
described In the avlan egg by Romanoff & Romanoff (1949).
The part~ally complete eggs discovered in Utah are of Class A. Two of
the best specimens were found imbedded in soft sandstone, standing on their
small ends with their long axes vertically disposed. This is in the same position,
relative to the mother, as were those described from South China by Chung-
Chien (1965). This probably indicates the~r locat~on as the same, or approxlmately
so, as that of their orig~nal deposition.
External APPeardvzre.-These eggs have a major equatorla1 diameter of
75 mm. and a calculated or restored total length of 160 mm. These dimensions
are necessarily approximate due to deformation of the shell. The shell thickness
is variable from 0.80 mm. et the equator to 1.70 mm. at the poles. Such
thickness var~at~cn In reptillan eggs of a non-spheroidal shape was noticed by
V. van Straelen in 1928 when he was concerned with varlous methods of
fossll egg identification.
Some Class A fragments collected exh~bit falnt color mosalc on the~r
external surfaces. Th~s pattern is delicate In Intensity and IS composed of two
or more sh~ades of h~gh,t tan end may penetrate the shdl to a depth of 0.25 mm.
It exists as a di'stinct periphenal zone in the outer shell and this layer may
separate from the remainder of the shdl by weatherrng. An eroded surface
of this zone ind~cates the mosaic is related to a crystalline structure

CRETACEOUS DINOSAUR EGGS 61
Pores.-Respiratory pores piercing the external surface of Class A shells
are distinct from those of the other two classes. The mouth of each pore is
somewhat depressed intto he shell surface and is elongate in a manner parallel
to the length of the egg. Some varieties of this class display only single
moukhed pores whi'le others may exhibrt twin pores as wel,l. Depressed edges
of these double openlngs may be in contact, or very neat each other, or may
be separated by a distan,ce equal ko the major diameter of one pore opening.
Both elongate openings In each pair have a common axls which is parallel
to the length of the egg. Surface distribution of pores In all three classes
appears to be random with their occurrence ranging-from 3 to 35 per square
cm. (In bhe case of the avian egg, Romanoff and Romanoff (1949) olbse~ed
that pores are generally $bundant on the blunt end omf the egg, near the air
chamber, and sparse on trhe polated end.)
Pore tubes, or ducts, penetrating from the surface of Class A shells do not
generally pass entirely through the shell without severe restriction at the can-
pact inner surface of the mammillary layer. On some Class A speclmens pores
may form in the exterlor layers but end abruptly about m~dway through the
shell at an intermediate zone. Such pores where observed are straight cylindrical
tubes. C h B shel'ls exhibit some simllar tubes of fairly constant dlameter
passing entirely t'hrough the shell.
Internal Appearance.-The general appearance of the mammillary or inner
surface is one of compact units with mammillae of various lengths and conical
in shape. Each mammrllae is compressed against its neighbor with their contacts
forming a reticulate pattern. The avecage diameter of the marnrnrllae is 0.12
mm. with the range bei,ng from 0.06 mm. to a maximum dbarneter of 0.18 mm.
The ratiform pattern of the mammlllae walls in eroded specimens is broken
occasionally by internal openings of pore tubes leading from the exterior of
the shell. These openings, usually sub-circular in outlrne, vary a good deal in
shape and may even resemble a trhree or four pointed star. Diameters of these
internal openings vary according to the different shapes they assume but
average from 0.06 to 0.12 mm. There appear to be no spaces between the
mamrnillae to provide for an ~ntermarnmillary ventllatlon system such as that
of Class C shells or of certaln fossil birds, as for example in the Struthionidae
(Sauer, 1966).
The mammillae of Clars A shells do not represent the beg~nnings of single
spheroliths rising to the surface but instead appear as a distinct lower zone.
The weathered edges of some speclmens dlsplay a high degree of stratification.
On one example (Plate 4, fig. I), the mammillary layer IS 0 52 mm. thlck and
is overlam by a succession of twenty or more alternating soft and resistant
layers of variable thickness. Several of these outer layers have separated from
the shell revealing the exposed, more Interior surfaces to be similar In appear-
ame to the outermost one. No color mosaic is present in thrs specimen. 1:ts
total thickness is 1 47 mm.
These peripheral layers origintated wlth deposition of differential amounts
of mineral and organic matrix during shell formation. These distlnct strata
therefore represent a tlme dimension in the production of the shell as con-
secutive layers of calcareous minerals were applied to the shell by the oviduct.
Environmental factors affecting the physiological stability and well-being

62 JAMES A. JENSEN
of the mother may account for the alternate hard and soft layers in this outer
portion of the shell.
Discussion.-All Class A material examined shows greater affinity with
that of fossil avian eggs than with eggs of dinosaurs as differentiated by L.
Thaler (1965), in his definition of the fundamental difference between eggs
of birds and di.nosaurs. He separates them upon the basis of the microcrystalline
structure of the shell. In the case of dinosaurs he asserts the existence
of single acicular ~pherolith~ic structures compr~sing the total thickness of the
shell. In bird eggs he accepts the customary definition of a rnarnmillary
spherolithic zone distinct from an upper arched or spongy layer. Judging from
the Utah materials we may assume he erred in this definition of dinosaur
eggshells simply because his study materials did not adequately represent a
wide enough range of dinosaurian eggshell structures.
The smooth-shelled eggs from the North Horn Formation are assumed to
be reptilian because of their size and late Cretaceous age but the interating
similarity between them and c6rt.ain fossil bird eggs cannot be denied. The
eggs of the extinct Tehary bird Aepyornis (von Nathusius, 1879) exhibit
strong similarities to some of the Class A materials described herein.
Class B
External appearance.-This group includes all specimens which exhibit a
nodose, or nodular surface expressed above the spheroidal surface of the shell.
(Plate 2, figs. 1, 7, 8; and Plate 3, figs. 2, 6).
Variation in this class ranges from those shells having simple independently
situated spherical nodes to those with elongate, extended nodes which wander
together to form ridges. One ~peaimen (Plate 3, fig. 2) dissplays simple
spherical nodes rising from a delicately sculptured surface having sparse and
indistinct pore openings. Another variety (Plate 3, fig. 6), with numerous
distinct pores, has elongate nodes merging to form meandering ridges with
individual spherical to sub-spherical nodes variously arranged in their midst.
Pores.-External pores of Class B shdls are not depressed Into the surface
as is common in Class A but rather the edge of each orifice is e~ther d~stindly
fllat or has a low rlng or collar remineiscent of a low crater surrounding the
opening. These openings are genemlly circular but may be subcircular with the
deviations being arcuate expansions of a circle rather than subc~rcular restrictions.
The average diameter of bhese circular orifices is 0.24 mm. with an
&served range of from 0.16 to 0.28 mm. The tubes leading directly from the
pores to the internal face of the mammillary layer are quite uniform in diameter
ranging from 0.10 to 0.20 mm.
Internal appeara~zce.-The surface of the mammillary layer has a coarse,
loose appearance when compared with Clan A specimens. The mamrnillae vary
in length and diameter from points to well-rounded cones of 0.24 rnm. diameter.
In some eroded specimens the cap of richly organic material is lost, leaving
ends of the mammillae with a concave surface. Examination under polarized
light indicates that the mammillae occupy a zone distinct from the spherolithic
peripheral zone and are from 0.10 to 0.18 mm. in length.

CRETACEOUS DINOSAUR EGGS 63
Class C
External appearance.-This class includes those specimens having a sculp
turd shell surface wherein the pattern is developed wisohin the peripheral
surface of the shell (Pl,ate 2, figs. 2, 5; Plate 3, fig. 4) rather than being
raised above it as in the case of Class B.
The external shell patterns of this class are varied in appearance and are
produced by indentations ranging from single inverted cones or pits to elongate
sub-spherical basins which may combine with other depressions to produce a
deeply stippled effect. The areas between the pits, slots and channels are
always convex-to-ridged leaving no evidence of the pheripheral arc as is the
case of Clms B. The bottoms of the pits and cones are not always uniformly
depressed on a radial hine but may sink i,n an irregular fashion to depths halfway
through the shell.
Pores.-The pore tubes enter between the spheroliths and thus penetrate
the shell on a line discordant with a radial line through the egg. Some of the
pits, which appear to be the equivalent of pores in the other classes, expand
Into tear-drop chambers midway through the shell. These internal chambers
are very common in this cl,ass and open through small ducts into the intermmiml,lary
ventilation system below. The shell has gross spherolithic crystal-
11,ne structures whlch appear to rlse from the points of the mam~llae to the
exterior surface of the shell resembling the "fundamental units" of Thaler
(1965) in his differentiation of dinosaur and bird eggshell structures.
Internal appemance.-The mammillae normally appear as truncated cones,
ranglng in diameter from 0.08 to 0.22 mm., and are loosely associated, allowing
for an inter-mammillary ventilation system. In some specimens (Plate 3, fig. 3),
caps or pinIts of the mammihe appear to have been eroded away leaving a
shallow depression In the end of each mammillae. In some fragments an oca-
sional inter-mammillary chamber rises to join variously with the mld-shell
cavities or pore tubes from the surface. The entire shell structure is much less
compact than that of either of the other two classes.
DISCUSSION
One very interesting aspect of rhe study of dinosaur eggs is the possibility
of so1~1,ng a,t least part of the mystery obscuning the rapid world-wide dlisappearance
of such a large group of diversely adapted an~mals. Var~ous authors
have speculated on the fate of the egg as posslbly representing a key to the
end of these domlnatlng rept~les of the Mesozoic, largely because of development
of unfavorable environmental factors which would increase their prehatching
mortality rate. After all, an egg cannot seek shelter or instinctively
retreat from its predators or in any way adjust itself physically to its surroundings
once It has been deposited In the ground by the mother. On rhe
other hand the possibility of environmental factors affect~ng the mother in an
unfavorable way so as to curtail successful egg production has not been overlooked.
L. Thaler ( 1965 ) postulates that sharply fluctuating temperatures,
which produced temporary but crit~cal cold waves, were a factor In reptilian
extinct~on slnce he assumes that the~r metabol~sm and egg production would
be adversely affected by such all environment. Other authors, as cited by Jepsen
(1964), 'have s~ . gested that destruct~c,n of the great reptile eggs by developing

64 JAMES A. JENSEN
mammals may have sounded their death knell. In any event, the egg, slnce ~t
symbolically at least represents the propagation of the race, will contlnue to
fascinate serious students, as well as an endmless cham of speculators, as belng
an Important factor in all studies of dinosaur extinction. Fut'hermors, ~t fol-
lows that future dlscover~es of eggs and continued detalled studies of them are
Imperative .f we are to completely understand the sudden departure of one of
the greatest ruling anlmal groups in earth history.
INDIVIDUAL EGGS AND WEATHERED CROSS SECTlOh
FIG. 1 -Weathered edge of Class A speclmen d~splaylng the lower speroltth~c mamm~llaq
zone and the upper stratifled zone, x 15.
FIG. 2.-Upper portion of an egg removed from ~ts matrix. The major equator~al d~arneter
is 75 mm. with the length of a complete egg belng approximately 160 mm Flgure
nat. slze.
FIG. 3 -Sect~on of soft sandstone matrix contalnlng the egg (f~g I), on the r~ght of
the f~gure, and a crushed egg ~n a hor~zontal pos~t~on tn the foreground A third egg,
w~th ~ts lnterlor excavated, on the left of the f~gure. Base of photograph 1s approxlmately
15 inches across.
EXTERIOR SHELL STRUCTURES
All photographs x 15
FIG I -Class B, nodose or nodular surface The pores are sparse and indlst~nct w~th
the surface belng roughened by eros~on.
FIG. 2.-Class C, sculptured surface. The pore tubes penetrate downward from the depths
of the ~rregular pits and cavities
FIG. 3 -Class A, smooth surface. Closely assoc~ated tw~n pores are vtsible, with two
single pores v~s~ble at the upper and left edges of the flgure, displaying the~r oval
shape.
FIG. 4.-Class A, smooth surface. The tw~n pores v~s~ble are spaced at a greater d~stance
than those ~n f~g. 3. Slngle pores are also v~s~ble.
FIG. 5 -Clas.s C, sculptured surface. This speclmen exh~blts a tar~ously p~tted surface in
contrast to ret~form surface pattern of the Class C specimen in f~g. 2. The pores
cannot be d~sb~ngu~shed from the small p~ts slnce the pores open downward from
the bottoms of the larger cavit~es.
FIG. 6 -Clu.fs A, smooth surface The surface is obscured by a th~n calcareous coatlng
FIG. 7.-Class B, nodose, or nodular surface The pores are very d~st~nct w~th several
rlslng directly through a node A general alignment of the nodes IS apparent.
FIG. 8.-Class B, nodose surface. Some of the pores exh~b~t
a low rlng or collar around
the orifice. The arcuate extension of the pore d~ameter IS present ln several open-
ings. The nodes are aligned ~n a general way

JENSEN PLATE 1
DINOSAUR EGGS

PLATE 2 JENSEN
EXTERNAL VIEWS OF DINOSAUR EGGSHELLS

JENSEN PLATE 3
EXTERNAL AND INTERNAL VIEWS OF DINOSAUR EGGSHELLS

PLATE 4 JENSEN
CROSS-SECTIONS OF DINOSAUR EGGSHELLS

CRETACEOUS DINOSAUR EGGS
EXTERIOR-INTERIOR VIEWS OF THREE FRAGMENTS
All photographs x 15
FIG. 1.-Class B. Mammillary or internal surface of specimen In figure 2. A chamber is
vis~ble in the upper left region of the figure. The mammillae appear as a more
or less compact mass.
FIG. 2.-External surface of f,~gure 1. Simple spherical nodes appear on a delicately
sculptured surface with few pores vis~ble.
FIG. 3.-C1a.r.r C. A low relief, sculptured surface in contrast to figures 2 and 5 of Plate
2 Some of the darker cav~ties descend into the Interior structure of the shell.
FIG. 4.-External surface of f~gure 3. The richly organic caps of the mammillae have
been eroded away leaving a shallow depression at the internal or prox~mal ends of
the mamm~llae. The mammillae are loosely assoc~ated with angular cav~ties and
chambers in their m~dst allowlng for inter-mammillary ventilation
FIG. 5.-Class B. Nodular surface. Internal surface displaying well-preserved mammillae
which are cone shaped and of irregular lengths. Small spaces are present between
them, but they are more compact than those of Clars C in figure 3.
FIG. (,.-External surface of f~gure 5. Nodes have elongated and are jo~ned In some areas
to form r~dges, with the pores of various diameters randomly disposed amongst
them Upper left border of specimen has been fractured by eroslon showing three
d~stinct layers.
EXPLANATION OF PLATE 4
RADIAL AND TANGENTIAL CROSS SECTIONS
FIG. I -Ch A, smwth surface. Pore tube is V J S J ~ at ~ right end of section where it
penetrates from the surface to a dark zone slightly less than midway through the
shell. Examinat~on under polar~zed light reveals this shell to be composed of two
rather distinct zones of crystallization similar to that of birds. The zone below the
pore tube 1s composed of a dark and a light band, the difference being the result
of the presence of different~al amounts of organic materials. Strat~fication is visable
In the upper zone but not In the lower one x 15.
FIG. 2.-Class A, smooth surface. The comparatrvely simple structure of th~s type demonstrates
the variation within Clmr A materials. x 15.
FIG. 3.-Class B, nodose or nodular surface. A polarlted rnicroscop~c examination defines
a simple spherolith~c structure. Stratification is due to organic materials. x15.
FIG. 4.-Class C, sculptured surface. The spheroliths rislng from the mammillae to the
surface of the shell are visible in thls class. A pore tube can be seen to expand
continually from the surface to the mammillary region near the right end of the
figure. A well-developed inter-mammillary ventilation system is apparent. x 15.
FIG. >.-Tangential section through a Class C speamen, 0.05 mm below the peripheral
surface. The black areas are the deep pits and cones which penetrate, in some speci-
mens of this class, to a depth of one-third the shell thickness. x 20.
FIG. 6.-Clars B, nodular surface. Tangentla1 section on a slight angle to the periphery
of the shell The left area of the figure d~splays the uncut surface of the mamm~llae
while the right area shows a cut through the manlmillae on an angle beginning in
the middle of the figure and reaching a maximum depth of 0.05 mm. in the upper
right hand corner. Inter-mamrnillaq chambers are visible at the beginninn of the
cut in m~d-figure but have disappeared before the maximum depth is reached. x 20.
FIG. 7.-Class A, smooth surface. Same type cut as figure 6 The compact mammillae of
thls class are very shalloxv, as can be observed In the right area of the figure,
wherein they disappear almost immediately as the angular cut begins. The deepest
point of the cut 1s in the upper right hand corner of the figure. No rnter-rnammrllary
ventilat~on system is vls~ble. x 20.

66 JAMES A. JENSEN
One of the reasons fossil egg deposits are seldom found, compared wlth
the frequency of skeletal remalns, may be that the mother was probably very
discr~m~nat~ng ~n her Choice of a "laying" spot. The fossil eggs from South
Ch~na (Chung-Chien, 1965) demonstrate a highly developed technique of
depos~tion by the mother. Various nests were found with the eggs d~splayed
in a rather interesting geometr~c arrangement. They are radially arranged with
the axes of the central eggs dlsposed In a vertical fashion. If the central eggs
were deposited first then each sucsesslve addlitlon was made In a circular
fashron with the axes of the eggs oriented toward an imaginary point somewhat
above the top of the nest.
The fossll eggs of Provence, France (L. Thaler, 1965), seem to ~nd~cate
a different and simpler method of deposition. Thaler reports these deposlts
were made with the eggs ly~ng In an interrupted linear series, w~th each egg
in a horizontal positlon relative to its long axis, rather than a single circular
radiating nest as was found in South China.
The locality for egg laying in each case appears to have been carefully
chosen and the event Itself was no doubt an exercise of great care. Modern
reptiles likew~se make a careful chaice of a "lay~ng" area and In both recent
and fossil cases such lay~ng grounds pro'bably are, or were, not plent~ful or
extensive In any one reglon. It must be thls factor then, whlch partially explains
the rar~ty of foss~l egg beds In eroded, or mountainous reglons, as such desirable
spots will now be less ev~dent than the rdatively continuous flood-plain or
channel deposits which contain abundant skeletal remains.
Another factor In the rarlty of fossil egg beds 1s the frag~le nature of the
eggs themselves If redepositlon of the egg-bed sediments occurred prior to
final burial, the eggs would be largely destroyed by fragmentahon and
abrasion, whereas skeletal remains, because of their more massive strength and
durable bony structure, would be preferenhally preserved in reworked sedlments.
Eggs are never structurally connected to the skeletons from which we
der~ve our phylogeny so it appears that accurate assignment of an egg to a
speciflc skeleton cannot be safely made unless definable embryon~c remains are
preserved within the shell.
In all comparisons of fossll birds and reptiles, and thelr eggs, we must
bear in mind the physiological differences between the~r modern representatives,
particularly In their varying rates of metabolism, and assume there was some
similar difference separating the extinct forms. In this assumption, however,
we must be careful for ~f birds developed from reptillan ancestors, which is
the generally accepted no'tion, then there must ex~st a broad zone of functional
adaptation in the line of descent wherein the transition was made from the
sluggish, low metabolic rate of reptiles to that of birds-the highest rate of all
animals. If birds were in fact derived from an egg-laying reptillan ancestry,
khey may have produced eggs in their earller stages of divergence very much
like those of their reptili,an neighlbors. Also, ~f a fundamental difference d'oes
exst between eggs of fossil birds and rept~les, such as the dinosaur, where in
the metabolic transition will this difference become evident?
The or~gin of birds, and certainly the history of their development, IS yet
qulte obscure so we must be cautious in sett~ng up any means of identifying
eggs w~th skeletal remalns found in Mesozoic sediments.

CRETACEOUS DINOSAUR EGGS 67
It is hoped that further investigation of the Upper Cretaceous sediments of
Utah may provide additional materials for study relating to the story of fossil
eggs.
REFERENCES CITED
Chung-Chien, Young, 1965, Fossil Eggs from Nanhsiung, Kwangtung and Kanchou,
Kiangsi; Peking, China, Contrib. Vert. Paleont. Peking Nat. Hlst. Mus., no. 2, p.
141-170, 19 pl. (Chinese & English).
Straelen, Victor van, 1925, Les oefs de Reptiles foss~les; Bruxelles, Palaeobiologica,
p. 295-312, 3 pl.
Thaler, LOUIS, 1965, Les oeufs des Dinosaures du Midi de la France livrent le
secret de leur extinction; Paris, F. Dunod, Science Progress-La Nature, Feb., p. 41-48,
11 figs.
Jepsen, G. L., 1931, Dinosaur Egg Shell Fragments from Montana; Science, v. 73, no.
1879, Jan. 2, 1931, p. 12-13.
G~llnore. C. W.. 1946, Reptilian Fauna of the North Horn Formation of Central
Utah; U. S. Geol. Survey Prof Paper 210-C, p. 29-53, 14 pl.
Nathus~us, W. von, 1868, Uber die Hullen, welche den Dotter des Vogeleies umgeben;
Zeitschr. fur wissensch. Zaologie, Bd. 18, p. 225-270, pl. 13-17.
---- 1879, Betrechungen uber die Selektionstheorie vom Standpunkt der Oologie;
J. 'F. Ornith, v. 27, p. 225-261.
Romanoff, L. A,, and Romanoff, A. J., 1949, The Avian Egg; John Wiley & Sons Inc.,
New York, 918 p.
Sauer, E. G. F., 1966, Fossil Eggshell Fragments of a Giant Struthlous Blrd
(Strurhio orhanai, sp. nov.) from Etosha Pan, South West Africa; Clmbebasia,
Publ. Admin. S.W.A., no. 14, 52 p., 28 figs.
Manuscript received November 28, 1966

Geology of the Kingsley Mining District,
Elko County, Nevada*
ROGER STEININGER
Pennsylvania State University
aes~~ac~.-The Kingsley Mining District is located in Elko County, in northeastern
Nevada. The present study is an examination of the geology of the district, along with
an evaluation of the future mineral economics of the area.
A Tertiary stock of quartz monzonite has ~ntruded limestones of the Upper Garden
City Formation, producing a contact aureole of marble. The stock is cut by numerous
dikes of varying composition from leucorhyolite to quartz monzonite, but only a few
dikes extend into the country rock. A dominate joint pattern has resulted from cooling
of the intrusive, and has controlled emplacement of both dikes and hydrothermal veins.
Extrusive felsite porphyries form a large hill southeast of the district. Field and
microscopic evidence indicate that these are flow rocks.
The Kingsley Mining District has produced small quantities of copper, lead, silver,
gold, molybdenum, and marble, mainly during the late 1880's. Additional economic
development in the area seems doubtful, unless certain of the marbles can be marketed.
TEXT
Paw
Introduction ......................................... 69
Purpose and scope ............................ 69
Location and accessibility ................ 70
Geologic setting .............................. 70
Previous work .................................. 70
Present work ....................................
Acknowledgments ............................
71
71
Structure ............................................... 73
Gross pattern .................................... 73
Contacts ............................................ 73
Internal structure ............................ 74
Sedimentary structure ...................... 74
Sedimentary Rocks ................................
Ordovician System ............................
Quaternary System ............................
75
75
76
Igneous Rocks ......................................
General Statement ............................
76
76
Kingsley Stock ................................ 76
Dikes .......................................... 78
Extrusive Rocks ....................................
Field Relations ................................
80
80
Composition ...................................... 80
Texture ........................................ 8 1
CONTENTS
INTRODUCTION
Purpose and Scope
Conclusions ...................................... 8 1
Summary of Igneous History ............ 82
Metamorphic Rocks ............................ 82
General features .............................. 82
Metamorphic aureole ........................ 83
Causes of metamorphism ................ 84
Economic Geology ................................ 84
History of development ................ 84
Ore deposits .................................... 85
Properties .......................................... 85
Future of the district .................... 86
References Cited .................................. 88
ILLUSTRATIONS
Text-figures page
1. Index Map ................................ 71
2. Geologic Map ............................ 72
3. Structure Sections .................... 73
4.
5.
Rose Diagrams .......................... 75
Thin sections of igneous rocks.. 77
Plates
1-4 Surface features of the Kingsley
Mining District
.......................... following page 81
Until recently the only attention given to the Kingsley Mountains was
related to the Kingsley Mining District. The intrusive and related areas have
*A thesis submitted to the faculty of the Department of Geology, Brigham Young Uni-
versity, in partial fulfillment of the requirements for the degree Master of Science, May
23, 1966.

70 ROGER STEINlNGER
remained unmapped, and the geology was only superficially known. The pur-
pses of this report are to produce a geologic map of the intrusive and related
areas, to describe the geology of the ara, and t~ evaluate the economic Fen-
tial of the district in light of past mini,ng ventures.
Location and Accessibility
The Kingsley Mining District (Text-fig. 1) is located In the southeast
corner of Elko County, Nevada (Secs. 13 and 14, T. 26 N., R. 67 E., and
Secs. 18 and 19, T. 26 N., R. 68 E.), in the southern end of the Kmlngsley
Mountains. The area is accessible via U.S. Alternate Highway 50 from Wend-
over, Utah, or from Ely, Nevada. A maintained dirt road extends 14 miles
southeast through Antelope Valley, to the Kingsley Mining Distrlct (Text-fig.
I), from the Southern mine turnoff on U. S. Highway 50, 40 miles south
of Wendover, or 80 miles north of Ely.
Geologic Setting
The Klngsley Mountains form a north-south trending physiographic unrt
about eight miles long, and one and a half miles wide, lying in the northern
part of the Basin and Range Province. The mountains consist of Lower
Paleozoic sedimentary rocks, mostly limestone, but w~th some shales, all with
a gentle northeast dlp. During the Tertiary Period a mass of quartz monzonite
intruded the southern end of the range. An aureole of contact metamorphism,
and minor metals~zakion hlas developed assodilated wlth the i'ntruslon. Antelope
Valley (Text-fig. 1) is a graben which is filled wlth a thick serles of Cenozolc
alluvium. In the late Tertiary Period a thick sequence of volcanic rocks
covered parts of the valley and the southern end of Kingsley Mountains.
Subsequent erosion has removed most of these flows, leavlng only a few isolated
outcrops.
Prev~ous Work
The first geologic report that included the Kingsley Mining Dlstrlct was
Clarence King's United States Geologic Exploration of the Fortleth Parallel
(1887, V. I, p. 61, & V. 11, p. 483). HIS geologic map shows the western
half of the range consisting of "Lower Coal Measures" limestones, and the
eastern half consisting of interbedded white crystalline dolomites and broad
tabular masses of granitic porphyry of Archaean age. Both sedimentary units
are shown w~th a north strike, and a dip of 25" to the east.
A brief investigatison of the K~ngsley District, whlch included a limllted descript~on
of the geology of the ~'ntrusive, was publ~shed by J. M. Hill In 1916.
In 1957, B. F. Stringham presented a paper, which included description of
the Klngsley Stock, resulting from research on the porphyries In the Basin and
Range Province. R. L. Armstrong (1963) obtalned a potassium-argon date
for the intrusive, and Granger, et a/. (1957, p. 102-104, and Plate 1) gave
a br~ef description of the area, referring Po it as the Klngsley D~strict; most of
thelr information was apparently taken from Hill's 1916 paper. On thelr
geologic map (Plate 1) the limestones were indicated as undifferentiated
Paleozoic, and Precambrian rocks were shown at the north end of the mountains.
Three separate northwest-trend~ng Jurassic-Cretaceous lntrusives were
also mapped in the Klngsley Mountains. Work by the writer failed to sub-

KINGSLEY MINING DISTRICT. NEVADA
TEXT-FIGURE 1.-Index map of Nevada and of northeastern Nevada, showing location of
the Kingsley Mining District in Flko County.
Present Work
Field work was carried out during the fall and winter of 1965. Geologic
data were plotted on aerial photographs having a scale of 1:20,000. This
information was later transferred to a base map of the same scale.
Preparation and examination of thin-sections of samples comprised the
major portion of laboratory work. Descriptions of thin-sections were made
using a petrographic microscope and universal stage. Identification of the ore
minerals was made by means of microchemical tests and a metallographic
microscope.
Acknowledgments
The writer expresses appreciation to Dr. K. C. Bullock w'ho served as
thesis chairman, and offered helpful criticism throughout the whole study.

72 ROGER STEININGER
Oal Alluvium
Ogc Garden City Formation
Tv Tertiary volcan~c rocks
Tiqm Tertiory quartz monzonif e
Tiqmp Tertiary quartz monzonite porphyry
MQM Melanocratic quartz monzonite
-- - Quartz monzonite
Metamorphic Rocks
M Marble
T Tact~te
r Quarry -. Adit
Inferred cor~toct
TEXT-FIGLIRE '.-Geologic- rna1.l of the Kingsley Mining District. Elko County. Nevada.

KINGSLEY MINING DISTRICT, NEVADA 73
TEXT-FIGURE 3.-Structure sections through the stock of the Kingsley Mining District.
M, marble; Ogc, Ordovician Garden Clty Formation; Tiqm, Tertiary quartz monzonite.
Scale same as geologic map (Text-fig. 2).
Thanks are also due to Dr. W. R. Phillips who assisted with the petrographic
work. Dr. H. J. Bissell spent several hours in the field explaining the strati-
graphic sequence.
Acknowledgments are accorded Shell Oil Company who supplied the
aerial photographs.
STRUCTURE
Gross Pattern
The Kingsley Stock is a nearly homogeneous unit of quartz monzonite
(Text-fig. 2). The only deviation from this homogeneity is in the north-
western corner of the intrusive, where a knob of porphyry about 20 feet in
diameter was mapped. Conrad been the two rock types is ,expressed by
appearance of phenocrysts up to two inches long, lying in a ground mass
similar in composition to the main intrusive body.
Contacts
The contact with the country rock along the eastern side of the Kingsley
St& is covered by alluvium. In rhe Marble Hill area a gradational contact
exists between the stack and the country rock. Here the stock grades into a
zone of tactite, which in tur,n grades into a marble zone, and then into un-
altered limestone. The tactite zone varies from a few inches to a maximum
of 39 feet wide. Around the rest of the intrusive, contact between the stock
and marble is sharp, and does not contain a tactite zone.
FieI'd relations along the west side of the stock indicate that the contact
dips steeply. Quartz monzonite forms a nearly vertical cliff, with the country
rack contact near the base of the cliff (Text-fig. 3). In one adit along this
side of the intrusive, the contact dips 74" to the west. The contact along the
north and south sides of the intrusive appears to be moderately dipping. A
dip of 30" to the north was observed in mine #3 (Text-fig. 3).
Several saddles exist on Marble Ridge and Marble Hill, and i,n each of
these a body of quartz rnonzonite occurs, with a texture and composition

74 ROGER STEININGER
similar to the stock. These bodies can be traced into the main ~ntrusive, sug-
gesting that they are kongues of the stock. The term tongue IS preferred be-
cause they are actual extensions of the intrus~ve. Elongation of the lntruslve
is further supported by the joint pattern.
Internal Structures
loznt/ng.-Bo:h exfoliat~on and tenslonal joints occur in the intrus~ve.
Throughout the K~ngsley Stock the exfoliation type 1s prominent, probably
related to release of the overlying load. . -
A dominant tenslonal joint set IS apparent in all the exposures (Plate 2,
Frg. 1). This pattern becomes more striking when the att~tudes are plotted
on a rose d~agram (Text-flg. 4-A). A dominant dlrect'ion of N. 40" E., with a
secondary set of N. 30" E., 1s typ~cal in the lntruslve. DIPS of both sets are
nearly vertical, wlth an extreme variance from 75" W to 75" E. These sets
are approximately parallel to the elongat~on of the stock. Emmons (1939,
p. 23) relates this type of fracture pattern to a pluton elongated In one of
two horrzontal dlrnenslons. Thls fits well with the observed relationships between
the ~ntrusive and country rocks in the Klngsley area.
Dlk1e.r and ore zw1~2s.-Rose dlagrams B and C of Text-flgure 4 represent the
general orientatton of d~kes and ore verns in the Kingsley District Both
features are roughly parallel to the domlnant fracture patterns, suggesting that
thelr emplacement was controlled by earher jointlng As the dlkes and velns
pass from the intrus~ve Into the marble, they malntain the11 orlentation,
parallel to a prominent jo~nt set In the mrrble (Text-flg. 4-D). Such a sltua-
tion would be expected ~f the quartz monzonite was close to the surface under
the metamorphic areas, for the jolnt~ng system developed in the Intrusive
would be transmitted upward into the cover rock (Emmons 1939, p 23).
This effect would decrease with dlstance from the lntruslon. Plate 1, flgure
1, shows strong jolntlng in the marble, suggesting nearness to the sto-k be-
neath the exposed marble.
lnclurzotz~.-Inclus~ons of melanocrat~c quartz monzonite are relatively abund-
ant wlthin the western half of the stock. They appear as dark colored ellip-
soidal lumps weathering out of the quartz monzonite. The ~nclusions are as
large as one foot long and six Inches wide, but occur as small as to one inch
In dlameter (Plate 1, fig. 2). Generally they occur In maximum numbers
along the extreme western boundary, and decrease In abundance toward the
center of the intrusion. They are completely lacking from the center to the
eastern margin.
Fcdult~.-Although field relat~ons strongly suggest the lack of faulting rn the
Kingsley Mln~ng Distr~ct, such structures cannot be completely discounted
because of the large area of the in'trusive now covered by wearhered quartz
monzan~te debris.
Sed~mentary Structure
Regionally tbe limestone of the district strikes N. 32"W., and dips 11"
to the northeast. This general attitude persists around the intrusive except for
the eastern side of Marble Hill, where folding has produced a small west-
ward plunging a,nticl~ne. Rocks of the northern limb dip about 13" to the

KINGSLEY MINING DISTRICT, NEVADA
TEXT-FIGURE 4.-Structural trends within the Kingsley Mining District. A, joints in
stock; B, dikes; C, hydrothermal vnins; D, joints in the contact zone of the intrusive
with country rock.
northwest, and those of the southern limb as much as 50" to the southwest.
This structure is completely lost in the altered zone of Marble Hill. The
structure could have resulted from doming during Intrusion of the quartz
monzonite. The marble zone can be traced around the intrusive, so that
Marble Hill is not a xenolithic body, but outside the Kingsley Stock.
SEDIMENTARY ROCKS
An incomplete section of Lower Ordovician rocks, consisting of a thin
sequence of the Upper Garden City Formation (H. J. Bissell, personal com-
munication, 1966), comprise the only exposed sedimentary units in the mapped
area.
The writer was primarily concerned with the igneous and metamorphic
rocks, and economic geology of the district. The only sedimentary rocks
studied are those which occur in close association with the intrusive.
Ordovician System
Garden Clty Formatiot2.-Approximately 500 feet of the Upper Garden City
Formation crops out around the eastern and southern base of Marble Hill, and
along the nokh s~de of Marble Ridge. In the proxim~ty of the Kingsley
Stock the formation has been altered to a pure marble.
The format~on consists of a calcarenite within the mapped area, in beds
three to five feet thick. These units are medium- to dark-gray, weathering to
a gray-brown with patches of red-brown chert. As a result of weatheping, thlin
shale partings stand out as wavey ribs. Thinly-bedded calcarenite, from one
inch to six inches thlck, occurs between beds. In the region of the contact

76 ROGER STEININGER
aureole the formation grades into a marble, characterized by an increase
in grain size, and bleaching of the limestone.
Petrographically th,is formation is rather simple. The limestone consists of
grains of sparry calcite ranging from 0.1 to 1 rnrn. in size. Small areas of
organic material, possibly dead oil, are scattered throughout the calcite. Each
gmin is unstrarined, suggesting recrystalllzation has occurred at some t~me
during its geologic history. A cloudy appearance to the grains can be related
to recrystallization of micrite to sparry calcite. Presence of organic material
indicated that this recrystallization was not related to the intrusion. Recrystal-
lization due to thermal metamorphism would produce bleaching, driving out
organic material.
Quaternary System
Antelope Valley contains a sequence of sediments derived from the sur-
rounding mountain ranges. These consis! of unconsolidated alluvium and
bajada deposits.
IGNEOUS ROCKS
General Statement
Several types of igneous rocks are found within the mapped area. Intrusive
rocks consist of quartz monzonitte, quartz monsonite porphyry, and dike rocks,
ranging from leuco~hyal'ite to quartz monwnite, all of which appear to be
genetically related to the Kingsley Stock. Extrusive igneous rocks in the area
consist of felsite porphyries. The Kingsley Stock is composed of a homogeneous
body of quartz monzoni'te. The only exception is a small zone of quartz mon-
zonite porphyry characterized by large phenocrysts of white orthoclase. Most of
the dikes in the district are composed of quartz monzonite porphyry, and these
are the only ones hhat intrude the country rocks. Numerous small leucorhyolite
dikes and a few melanocratic quartz monzonite dikes are also found within the
stock. A large outcrop of extrusive felvite porphyry occurs about one-half mlle
southeast of the Klngsley Stock. It forms a hill about 400 feet high, 2850 feet
wide, and 8000 feet long.
Kingsley Stock
The Kingsley Stock cmps out in a rough square, about one mile acm. The
intrusive generally forms a topographic low, relative to the adjacent limes,bne.
Relative ease of erosion is expressed along the contact between the stock and
the country rocks, ai~d in parts of the stock that have been intruded by dikes, for
in most places the contact is in a valley. Most of the dikes are found on the bps
of smil hills in the inltrusive because of thir relative resistance to emion.
Weathefling of the quartz monwnite turns the light-colored rock to a rust-brown.
Mmy inclusions of melanocracic quartz monzonite throughout the western half
of the i,ntrusion stand out as elli,psoidal nobs as a result of differen~tial weathering.
Evi,dence of bhe magmatic origin of the intrusive is readily seen in the field.
Except for a small area on Marble Hill, the contact is sharp and discordant.
Lack of xenoliths similar to country rock suggest the present exposure of quartz
rnonzonite represents a moderately deep level of the intrusive.
-
Ouavtz Monzonite.-A white to llighlt gray quartz monzonite is the dominant
rock type in the Kingsley Stock. Serrated grains from 0.5 to 4.0 mm. across have

KINGSLEY MINING DISTRICT, NEVADA 77
TEXT-FIGURE 5.-Line drawings of bleached photomicrographs of intrusive igneous rocks
in the Kingsley District. All are x 135. A, Quartz monzonite stork; B, Autoliths
within the stock; C, Quartz monzonite dike. Minerals labeled ~nclude: Q, Quartz;
B, biotite; P, plagioclase; H, hornblende and other dark minerals. Area between
phenocrysts is groundmass.
a hypidiomorphic-granular relationship. Generally the largest crystals are biotite
and plagioclase, with smaller sobhdral grains of hornblende and still smaller
euhedral quaatz, orthwl~ase, and opque minerals.
Essenbial minerals, determined by microscopic exminabion, are oehoclase,
andesine, and quartz (Text-fig. 5-A). Andesine grains are the most euhedral
and range in size from 1 to 4 mm. An average composition of An,, was determined
from he analysis of twenty-three thi'n-sections comprising a representative
sampling of the stock. Oscillatory zoning is common wimth a core of An,, and
a rim of An,,, thus representing a normal zonation for the crystal as a whole.
A11 plagioclase shows albite winning with subdinate Carlsbad and pericline
twins. A few crystals are saussuritized, but no general relationship can be drawn
regarding their position in the stock.
Accessory minerals include biotite, anphsibole, apatite, sphene, zircon, and
magnetite, the latter four comprimse about 1% of the total rock, and are listed as
"athers" in the following tables. B,i&ite occurs as subhedral grains up to 4 mm.
in diameter and is pleochroic with Z-dark brown and X-light brown. A few
crystals are sl'ightly altered to chlorite along the cleavage plan-. Hornblende
forms sufbhedral grains from 0.5 to 1.5 rnm. in length which are strongly
pldroic, from dark green (Z) to light green (X), and have 2V, = 79",
and CAZ = 18". A few cryds have a18tered to bidite in their centers.
The folIowing percentage of minerals represents an average composition
of the main rock type in the stock.
Orthoclase
Andesine
Quartz
Hornblende
Biotite
Others

78 ROGER STElNlNGER
Quartz Monzonrtr Porphyry.-(Plate 2, fig. 2)-The groundmass has essentially
the same compsibion and relationsh,ips as the rest of the stock. The difference
between these two zones IS the orcurrence of euhedral orthoclase in
the form of phenocrysts up to two Inches in length. 'Th~is zone has the follow~ng
composrtion :
Orthoclase 44y;
Andes~ne (An,,,) 25%
Quartz
Hornblende
24yh
(2V, = 84O, CAZ = 26")
B~otite
5%
1 yh
Others 1" /O
Il.lafrc 1ncluston.c.-(Plate 1, f~g. 2, and Plate 3, fig. 1)--Dark gray to black
ell~psoidal mafic inclusions are abundant throughou't the wetern half of the
stock. They occur singly or in swarms where the major~ty of the outcrop IS
cornpr~sed of the ~nclus~ons. In the field they appear to be homogeneous In
composiltion; contacts wlth the surrounding rock are sharp, the quartz monzonite
showlng no apparent ch,ange up to the contact. Pabst (1928) described
similar inclusions in the plutonic rocks of the Sierra Nevad'a, wh~ch he called
autoliths (= cognate xenblihhs) .
Microscopically (Tex-fig. 5-B) the mineralogy is the same as that of the
quartz monzonite. The dlifference lies in the grain size and compositional percenltage.
Mineral grams are between 0.1 and 0.5 mm. across, biotite, hornblende,
and plagioclase being the largest. The following average composition shows
the greater abundance of ferrormagnesiium minerals cjompred to the host
monzonite.
Hornblende (2V, 74", CAZ 12") 3570
Quartz 17%
Andesine (An,

KINGSLEY MINING DISTRICT, NEVADA 79
comprlse 53% of the rock; the remaining aphanltic portion is compr~sed of
quartz, crthoclase, and minor plagioclase, magnet~te, apatite, zircon, and sphene.
The average composibion of these dikes is as follows:
Orthoclase 347;
Quartz 31%
Andesine (An,,,) 27%
Biot~te 5%
Hornblende 25%
Others 1%
Alteration is very extenswe within these rocks. Most of the phencxrystic
and'eslne has been saussuriltized. Horniblcnde and biotite show all gradations
from fresh minerals to a mixture of chlor~te and opaque oxides.
Leucorhyo1rte.-This rock is composed of hypidiomorphic-granular orthoclase
and quartz, with mlnor amounts of ol~goclase, hornblende, biotite, and rnag-
netite. These minerals occur as gralns not greater th'an 0.1 mm. in slze. The fol-
lowing table shows the proportions of minerals present in these dikes:
Orthoclase 467&
Quartz 41 %
Okigwlase (An,,) 9%
Others* 27%
Hornblende
(2V, = 76", CAZ 14") 1%
Biotite 1%
*Mainly magnetite
Quartz and orthocl'ase are the largest minerals present, abut 0.1 mm. In
d,iameter, and have an anhedral shape. Oligoclase, hornblende, and bioltite are
smaller In slze, and dfisplay subhedral forms. Crystal shape Indicates that all the
minerals crystallized at approximately the same time.
Melarzocratrc Quarlz Monzonzte.-D~kes s~milar in composition to the autoli~hs
are found within the stock, but the~r occurrences are very limited. They differ
from the autoliths in having a porphyritic texture, and a flner grain size.
Phenocrysts of subhedral andesine, 1 and 4 mm. long, comprlse 10% of the
rock. The groundmass is composed of subhedral b~ot~te, hornblende, anhedral
orthoclase, and quartz 0.1 mm. In diameter. The average comps~t~on of these
dikes is:
Biotite 39%
Hornblende 24 c/,
Orthoclase 21%
Quartz 14%
Andesine (An,,) 10%
Others 2%
Owing to its larger size the andesine IS considered as havlng crystall~zed
first, followed by the biotite and hornblende, and lastly the rest of the minerals.
The only alteration observed within these dikes was mlnor saussuri'bization
around the edges of the plagioclase phenocrysts.

80 ROGER STEININGER
EXTRUSIVE ROCKS
Field Relations
Tentiary volcanic rocks are restricted to a h,ill approximmtely 400 feet
high, 8000 feet long, and 2850 feet w~de near the southeastern corner of the
Kingsley Mountains (Text-fig. 1). The outcrops appear outwardly to be composed
of a single flow, but upon close examtination three separate flows can be
disst~nguished. Each flow has the same general appearance, but at the base of
each of the upper two is a layer of v01can~1c rubble derived from the underly~ng
weathered volcan~cs. All three flows have a s~milar attitude, strlking N. 15'
W. and dipplng 21" E. Field relations suggest that they were draped over the
soubhern end of the Kineslev ", Mountains. Subseauent erosion has removed most
1
of the flows from the range, leaving only a few areas containing rocks similar
to bhose found In Antelope Valley and around the southern end of the Kingsley
Mountains. This theory is substantiated by mapping of the volcanics on the west
side of the K~nglsey Mountains by geologists of Shell 011 Company (personal
communications, 196>), where the extrusive d s have a westward dip.
Megascopically, the volcanic racks are aphanit~c, porphyritic and light gray
on a fresh surface, weathering to a red-brown. Most of the volcanics are slightly
vesicular, with the cawsties about 1 mm. in diameter.
Composition
Thin-sect~ons indicate a homogeneity of rock type throughout the whole
sequence. The average modal composition of the porphyritic felsite flows, as
compiled from ten representative thin-sections, is:
Andesine (average An,,) 11%
B~otite 1%
T~idymlite 2%
Opaque oxides* 2%
Hemti te 5 yh
Groundmass 79%
"Presen~t as grains larger than the groundmss
Andesine occurs as phenq* ranging from 0.5 to 1.5 mm. (Plate 4, fig.
1). Mmt are twinned, wilth the Carlstvad law being dominant over the albite
law. Oscillatory zoning is obvious in nearly every phenocryst, in addibion to
normal zoning with a are that is more calcic than the margimn.
The groundmass consists of a microcrystalline aggregate of sanidine and
opaque oxides. Plate 4, flg. 1 represents a typical groundmass containing an
average of 30% opaque oxides and 70% sanidine. Sanidine forms euhedral to
subhedral grains with opaque oxides fill~ng in interstitial spaces There is a
noticeable variation in groia size ranging from just above the microli,te stage in
a maximum of about 0.1 mm. There is a slight ofiientation of minerals of two of
the samples. Study of the elongation in or~ented thin-sections Indicated a flowage
in either a northeastern or southwatern diirection. Presence of tr~dymilte
indicates that the mks formed at a relatively high temperature, above 870' C.
The tridymite occurs as wedge-lhaped twins within the groundmass. These
crystals are among the largest whhin the size range of the groundmass. Biotite
under hsighly oxidizing condiltions has altered to a more stable mineral assemblage.
The alteration product is primarily hematite. Pl'ate 4, fig. 2 shows a re-

STEININGER PLATE 1
FIG. 1.-Jointing in the contact metamorphic zone.
FIG. 2.-Autolith in the stock.
OUTCROPS OF THE KINGSLEY STOCK

PLATE 2 STEININGER
FIG. I .-Jointing in a quartz monzonite dike that cuts the stock.
FIG. 2.-Porphyry zone within the stock
JOINTING AND PORPHYRY WITHIN THE KINGSLEY STOCK
ff

STEININGER PLATE 3
FIG. 1.-Leucorhyolite dike swarm in the stock with autoliths present.
FIG. 2.-Marble quarry on the south side of Marble Ridge.
DIKES AND MINES IN THE KINGSLEY DISTRICT

PLATE 4 STEININGER
FIG. I.-Felsite porphyry showing groundmass, and plagioclase phenocryst X 120.
FIG. 2.-Altered biotite wuth a biotite core remaining X 120.
PHOTOMICROGRAPHS, KINGSLEY nW"ICT

KINGSLEY MINING DISTRICT, NEVADA 8 1
action rim of hemat~te around a core of biotite. In all bhe thin-sections examined
not one biotite phenocryst was found that did nat show at least a partial reaction
rim of hematite. Only the larger phenocrysts have a core of unaltered biotite.
Texture
The most striklng aspect of the texture is its porphyritic nature. Phenocrysts
of plagiwlase, and altered b~otike in bhe general size range of 0.5 to 1.5 mrn.
occur in a groundmass of 0.1 m. or less. Phenocrystic minerals are subhedral
to anhedral in shape. The hematilte aggregates show only an approximation of
the origlnal biotite. Using textuwl terms as defined by Johannsen (1931, p. 49)
the groundmass is classified as p~lotaxitic-tra~hytic.
Conclusions
Recent work in the acidic extrusive igneous rocks of western Utah and
Nevada by many geologists has resulted in the wide use of the term ignimbri~te.
'lhk has led to loose applicabion of the term to many extrusive rocks in this
part of the ccuntry. Such was @he case at the onset of this study. After a field
and petrographic study of the fels~tes In Antelope Valley, the author concluded
ehat they are flows rather than welded tuffs. One wonders just how many of
the acidic extrusive rocks of western Utah and Nevada really are ignimbrites.
Reasons for calling the felslte a flow rock can be summarized in a table
comparing the characteriaics of igniimbni

82 ROGER STEININGER
Welding, distortion
and stretching
Pyroclastic orlgln rarely destroyed.
Foliat~on resulting from
stretching. Y & U shapes
around phenocryyts.
No pyroclastic texture, or
stretch~ng Slight flow structure.
Phenocrysts Feldspar, quartz, blot~te, hornblende,
and auglte.
Plagroclase, blotite, opaque ox-
~da. and hematite.
SUMMARY OF IGNEOUS HISTORY
The first ignecus event in the area was the intrus~on of the Kingsley Stock
during the middle Tertiary. Armstrong (1963) has determined a potasslumargon
date of 35 (-2, + 5 ) mlllion years for the stock. He has also obtained
a lead-alpha date of 41 million years, wh~ich puts the two dates In close approxrmation.
This would pl,ace the tlme of Intrus.ron In elther the late Eocene or
early Oligocene. From hlis work he suggests that the depth of intrusron was
10-15 thousand feet below the then emsting surface.
Lack of fault~ng In the immediate ccuntry rocks indicates that the lntruslion
was not controlled by faults dur~ng emplacement. The most probable mode of
emplacement was that of piecemeal stoplng and asslrnrlat~on.
During cml'~ng gravrtat~onal settllng of the early formlng ferromagnesium
and plagi,oslase mrnerals probably occurred, and produced a mafrc zone w~th~n
the stock. The maf~c dikes were likely formed by tapp~ng such a ferromagnesium-rlch
zone. Convection currents could conceivably exlst as the melt lost
heat, and could posvibly move parts of the maflc zone up to hlgher levels wlthln
the stock, thus produc~ng the autol~iths. An alternate hypthes~s for the formtion
of these inclus~ons relates to the~r small gram size and rich maflc comps~ticn.
A chill zone around the magma would be expected to conslst of an
aggregate of small s~zed, early formed minerals. Later Igneous activ~ty could have
caused a breakup of th~s chill zone, suppl~ng the material for the aubliths.
As the mdt began to solid~if~, a fracture pattern probably developed as a
result of tension due to contracti'on with coolrng. If the intrusive body IS
elongated, as suggested above, one would expect the domlnant joint set to be
the longitud~n~al pabtern that ex~sts. It was along these fractures that the majority
of the d'ikes were emplaced as the result of a later magma surge.
The last event that can be rel,ated to igneous intrusion IS formahon of
hydrothermal velns, the majoristy of which were emplaced along the dominant
joint set.
Some time after emplacement of the stock, a serles of three felslte porphyry
flows were extruded over the area. Neither the so'urce nor the age of these
flcws can be determ~ned ~11th the present information.
METAMORPHIC ROCKS
General Features
The sedimentary rocks around the Kingsley Stock have been subjected to
contact metasomatlsm and mrnor thermal metamorphism. A distlnct metamcrph~c
aureole has been devebped on the north and south s~des of the Intrusive.
The east side of the stock is covered by alluvium so that the extent of
mebamorphism IS undeterminable. Along th'e western margin of the intruslive the
auresole is a maximum of five feet w~de, and a minlmum of a few inches where

KINGSLEY MINING DISTRICT, NEVADA 8 3
limestone 1s in contact wilth the stock. The intensity of metamorphism decreases
away from the stock.
Three types of metamorph~c rocks cxcur wi@hin the contact aureole; they
are: dolomi~tic marble, marble, and tactite. A small zone of tactite exists along
the nor>hea.st side of Marble Hill, dolomitic marble is restricted to Marble Hill
and Mlarble Ridge, and the marble is located along the western side of the intrusive.
The greatest extent of metamorphism has developed in the Marble Hill area,
and a smaller yet significanlt zone along the sooth s~de of Marble Ridge. The
western contact has been affected by only a minor amount of metamorphism.
Metamorphic Aureole
Thermal metamorphism produced a rather impure, fine-grained marble, with
relics of unaltered limestone, along the western contact of the stock. The marble
is composed of a finely-crystal~line aggregate of calcite. The only change from
the calcarenlite is a slight bleachling and removal of organlc material.
MebmmCism has been active in product~on d a dolomitic rnarble in the
Marble Hill and lMarble Ridge areas. The parent rock probably was a pure
calcarenite, hence, the only source for bhe dolomitizing sclutlons was the
Kingley Stock. Calcite within the limestone has been completely changed to
dolomite. This would be expected during dolomitization, and Ramberg (1952,
p. 225) attributes this feature to the following:
The fact that dolomitization tends strongly to create rather purr dolomite
marbles with but minor amounts of calcite may be due to the interfacial energy
conditions between calcite and dolomite. It is likely that a dolomite nucleus does
not form so easily in contact with calcite grains as it does in contact with other
dolomite grains. Therefore, the dolomitization will most likely proceed in
such a manner that a pure dolomite rock develops rather than intermixtures of
calcite and dolomite marbles.
Dolomi,tic marbles in the area consist of an aggregate of dolomlite and about
5% pyrite. Dolomite graimns range in size from 0.5 to 2 mm., while the py~ite
is about 0.1 mm. acres's. The 1,atet;al change from dolomitic marble to calcarenire
is gnadahional, being expressed by increase in bhe amount of relsiat limestone.
On the outer limits of dolomitization only a vein or two extends into the limestone.
The pyri'te is di,ssemin.ated throughout the m'arble with no apparent
orienkabion.
A small zone of tacfiite exists along the northeast slop of Marble Hill,
and represents the highest grade of metamorphism attributed to the Kingsley
Stock. The tactite is chsaracterized by xtinol'ifte, and a complete lack of carbonate
minerals. The coatact between the hactite and bhe dolomitic marble is graddional
and expressed by a narrow zone of mixed dobmiste and actinolite. A gradlational
contact also exists between the tadi~te and the stock.
Megascopically, the tactite is light green, spotted by numerous white grains
of quartz. A typiJcal speaimen from rhis area has a modal cornpieion:
The actinoli(te is from 0.1 to 2 mm. in size, whereas the quartz ranges from 0.1
to 0.5 ntm. The actinolke occurs as radiating c~ystalline masses, witlh the quartz
fjilling the interstibia1 areas.

84 ROGER STEININGER
Causes of Metamorphism
Two disbinct types of mebmrphism appear to have been active in the
rocks around the Kingsley Stock. They are thermal metamorphism and contact
metasomatism. Structural control seems to have played a dominant role in
determining each type developed in the contact aureole.
. -
The jointing pattern in both the st~k and country rocks and the general
shape of the intrusive body seem to be the controlling factors in producing the
differenlt types of metamorphism. Areas where the dominant nontheast joints
(Text-fig. 4 A and D) extend outward into the country rocks also coincide
wibh areas of contact metasomatism. A general relationship exists between the
size of the aureole and the extent of the fracture pattern. Where the joints
die out, a metamorphic-limestone contact is found. It is felt that these joints
served as channelways for the metasomatic solutions. The projected elongation
of the stock places the country rock-igneous rock con.tact closer to the surface
in these areas. As would be exwed, the closer to the intrusive body, the
greater the amount of metamorphism. Sedimentary rocks around the eastern side
of Marble Hill dip directly into the st~k. This would allow additional paths
of ion m~igration, causing the h,igher degree of alteration.
Along the western boundary of the stock these structural relationships do
not ex~st, so that the rocks were relatively impermeable to ~onlc movement.
Thus, the only metamorphism that occurred was thermal metamorphism,
causing a bleaching of the rocks.
ECONOMIC GEOLOGY
History of Development
The Kingsley (originrally Kinsley) Mining District was first discovered by
Felix O'Neil in December, 1862, who named it the "An8tdope District." After
he was driven out by local people, @he district was rediscovered by George
Ki'nsley in 1865. By 1867 some 30 claims had been worked, with a Mexican
fwnsce in operation to process the ore. Ore running $64 to $93 a ton in silver,
and 0.5 ounces of gold was repocted during this period, but this mining activity
was short lived, and in 1872 the area was abandoned. In 1909 the Kinsley
Deve!opmentt Company reopened the area by starting a relatively large operation,
including a concentrating mill. This development apparently was not succm-
ful, and the operations were soon cu~tailed. Since then only sporadic activity
has been carried out in the distrid, with a Mr. Southam being the latest entry
into the mining ventures of the Kingsley District. The preceding description of
the Kingley District has been taken, for the most part, from Hill (1916), and
Granger et al. (1957).
Mr. J. H. Schilbing (Nevada Bureau of Mines, personal communication,
1966) states that production of the &strict as a whole has been: 102 ounces
of gold, 2336 ounces of silver, 31,711 pounds of copper, and 21,014 pounds of
lead. He says that this d'ata comes from a variety of sources, but is believed to
be essenltially complete. The present invesdgation of the district showed rhas
the only addition to bhis is a small amount of molybdenum and maable shipped
from the Southam properties. Recent production figures are difficult to obtain,
so much ok the production data is incomplete.

KINGSLEY MINING DISTRICT, NEVADA 85
Ore Daposits
Contact Deposits.-Replacement bodies containing scheelite are the only metallic
contact deposits in he area. Tungsten ore Mia lie in the d~lmitic marble,
near bhe contact with the intwive, in hhe Muble Hill area. Scheel'ite occurs as
a dissemination in hliized arm of the metamorphosed country rodcs. The de-
pits are all low grade and do not appear to have a large potential. It is doubt-
ful if these deposits could be worked profitably, even with reenactment of
federal government price supprt.
Vernr in Igneous Rocks.-A few veins of white bull quartz occur within the
inbmive. They are less than a foot wide, and never appear to be mre than ~ix
feet long, and contain pyrite, dhlalcopyrite, and small amounts of galena.
Prospectors have developed workings on all the exposed quartz veins. A
close investigztion of these indricated no increase in tenor with depth. Unless
they lead b some longer subsurface deposit, which is doub~ful, these veins will
never be large producers of ore.
Small amounts of copper mineralization have developed along the contact
been bhe st~k and several of bhe qurtz mnmnite dikes. Copper is present
in khe form of chryslocolla, probably forming from alteration of chalcopyrite.
Alil of these depits have been pmpectd with little or no success. It is doubtful
bhat these deposits undergo any increase in tenor with depth.
Veins in Metamorphosed Rocks.-The most important deposits of the district
ar- found in hydrothermal vei'ns in the metamorphosed rocks. Tension joints
wu~h small mnts of breccia have served as a host for emplacement by hydro
bhermal ~olutions. Siliceous soluriom containing copper, iron, lead, silver, gold,
and molpbdenum minerals were deposited in a gangue of quartz. rdpper is rhe
dornimn.t metal and was original.1~ chalcopyrite that has altered to malachite,
azurite, and chrysocolla in the ox~dized zones. Iron in the form of pyrite, witrh
minor hemabite, has alkred to limonite, forming gwans that cap all the veins.
Galena is present in the unoxid~ized mnes, wiihh ceruss~te being the oxidlizd
pduct. Cerargyri,te, native silver, and native gold have also been reported i'n
bhe district (Hill, 1916). Molybdenite is the mineral m,ined mmt recently in
the diutrict. The mineral assembl~age suggests that the ores are characteristic of
metothermal deposits. Of all the metals mentioned, the most important is
copper, with lead of secondary importance. Gold, silver, and molybdenum produation
has been small, wi'th silver the largest of the rhree.
All of these veins have been capped with a pssan making their Idion no
pmblem to the prospeator. Each of the veins has F, tested or exploited.
The future of bhe Kingsley Miming Dilutrict is held in these veins.
Nonmetallic Productr.--Marble, from the south side of Marble Ridge, recently
has been quarried for use as a building stone. Owing to ib highly fmctured
nature, the r d has been crushed to about one-half inch in size, and used as
buildling facing.
Properties
There has been little mining adivity iln the Kingsley Mining District in
recent years. Many of the older wu>rki,ngs are prtly or totally caved, and wee
not acmwiibk to the writer. Dm~ipions of such workings are largely taken from
Hilhl (1916).

86 ROGER STEININGER
Kingsley Cotzsolidated Mines Co. clrurnr (see Text-fig. 2, Loc. I).-The main
workings are about Q mile nor& of the mntact between the igneous and meta-
morphic rocks. A shaft 100 feet deep, and four adits comprise the major por-
bions of the mine. A vein striking N. 21° E. and dipping 55" to 60' E. was
worked, and consisted of a tight, barren fracture that had several openlngs up to
2 feet wide. The swells contained oxidlzed copper and iron minerals. Ghryso-
colla, malachite, and chalcocite were mined and milled on the property.
Morning Star Shaft (Text-fig. 2, Loc. 2).-Originally owned by the G. A.
Lowe estate, it was last worked by leasees, E. C. Rowland and John Fasano, In
1913. A 375-foot shaft in a vein that strikes N. 86" E. and dips 50" N., produced
mbachite, azur~te, and chrysocolla, with a little cerarbyrite and gold. The
Last min~ing venture was to ship the dump that carried $25 a ton ore in silver,
lead and copper.
Kzngsley Mnze (Text-f~g. 2, Loc. 3).-Caved at the t~me of Hlll's reprt;
he states that a deep shaft was sunk as ~ndlcated by the large dump. Only
mlinerals of economlc lmprtiance were capper carbonates.
Southam Mo/ybde)zr~nz Mule (Text-fig. 2, Loc. 4).-A no~theast striking vein
bhat dips 55O W. occurs within the metamorphosed rocks. The major cre
mineral is malybdenite, camping up to 35% of the vein. Capper minerals
scheelite, and galena are also present. At present this property is no: being
worked due to small tonnage.
Southam Marble Quarry (Text-fig. 2, Loc. 5, and Text-fig. 4-B).-A very
pure, hlighly fractured dulomitic mlarblc was recently quarried from two open
piits on the sourh side of Mavble Ridge. The material was crushed at the site,
and bagged for shipment. Several tons were shipped to Denver, Colorado, for
use as a facing cn Denver Federal Center buildings.
Other Prospects
The preceding is a sketchy dcscript.ion of mining activity of bhe district, but
it represents all the information available to the writer. The res: of the district
is dotted by many small prospect pits, adits, and shafts. None of these have pro-
dwed ore.
Future of the District
Ore bodies discovered to date in the Kingsley Mining District have been
sml~l, and generally, of low grade. Allkhough bhe region has been prospected
iNtavrnittently for over a hundred years, i8t has yielded less than $10,000
(Granger and c~khers, 1957); mostly in copper and lead, with minor gold and
silver. All past exploraticns have been on a small scale and guided solely by
surface exposures. At prcsent surface exposures aFpear to be mined out, and
h'ave nat led to dliscovery cf large ore bodies.
Occurrence of a large variety of metals within the dis,trict suggests that the
magma my have been relatively high in metal contenst. Thus, the only pcmible
future mineral devele~pment wculd be at depyh. Shcet of an extensive drilling
program, there is no dlirect method of datermlining the extent of subsurface
deposits, if any. As an indirect method cf determining extent of metallization
in tlhe veins; the writer undertook a detaileld study of ~heii gcssans, for gzsssns
should indicate their size and original mineralogy.

KINGSLEY MINING DISTRICT, NEVADA 87
All of the ore veins are steeply dipping so that oxidization has produced
a gossan with a mlnimum of "mushrooming," while length of the vein should be
faifihfully reproduced. None of the psans studied were over seven feet in
length, although several "trains" of cap rocks were c8bserved ~n the fleld. This
suggests that several veins of conviderarble length eximvt in the d,istrict but they
undergo considerable pinching and swelling, and oxidization has produced a
aapping gossan over the swells. Distances between swells are usually tens o'f
feet, sugge~t'ing the velns are narrow along much cf the~r lengkh. The wides:
gossan ln the Kingsley Drstrict IS about 11 feet x rm, but the majority are only
two or three feet wide. Slnce these cap rocks have undergone some "mush-
rooming," most underlying ore veins must not be more than a foot or two
wi'de. In areas that have been mined out under the gwans, slze of khe ore vein
can be determined. The widest vein seen was 4 feet wide, but the average width
of all veins is from 1 to 2 feet. Unless there IS extensive widening with depth,
liimle hope is held for larger subsurface depos,it.s related to these hydrothermal
veins.
In an effort to determine the original m~neralogy of the veins, a detailed
hdy of the limon~te boxworks was undertaken, as summarized in Bateman
(1950, pp. 258-259). The gcssans are composed dominantly of limonite, with
sulwordlnate wad, quantz, hematite, and secondary copper minerals. As a means
of checking the method, several adits in the unoxidized zone of the veins were
sampled and compared w~th informd~on obtained from overlying gossans. A
very close correliation was found. Motst of the larger gossans and several of the
smaller ones were studlied, and in these the dominant leached mineral was
chalcopyrite, wifth smaller amounts of bornite and galena.
A.
Development of supergene enrichment hinges on the ability of the leached
minerals to leave the oxidized zone and be deposited in the zone below. The
fullowing react~ons are involved in the leachlng of those ore mlnerals present in
the ore veins of the Kingsley Distaict.
The leaching of pyrite will produce the needed solvents (Fern.,, H,SO,, and
Fe(OH),) for leaching the other minerals. Chalcopyrite, bornite, and galena
will be leached according to the fol~lowing reactions.
chalcopyr~fte-CuFeS, + 2Fe,(SO,) = 5FeSO, -+ CuS
CuS + Fe(SO,), = CuSO, + 2FeSO, + S
galena-PbS + Fe,(SO,), + H,O + 30= PbSO, + 2FeS0, +
H,SO,
bornite-Cu,FeS, + Fe,(SO,), = CuSO, -k 3FeS0, + CuS
CuS + Fe(SO,), = CuSO, + 2FeS0, + S
Precipation will occur in the presence of dolomitic marble almost as soon as
the sulfate is formed. Such minerals as azuri,te, malachite, chrysocolla, and
cerussite will form. Thus one would nat expect to fi'nd a major supergene en-
nched zone below the oxldized zone. The above end products have been
observed within +he oxidized zone, adding weight to the conclus~on that an
extensive supergene enriched zone is pmtmbly lacking.

88 ROGER STEINlNGER
REFERENCES CITED
Armstrong, R. L., 1963, Geochronology and geology of the eastern Great Basin in
Nevada and Utah; Unpublished Ph.D. d~ssertation, Yale Univ., 241 p.
Bateman, Alan hl., 1950, Economic mineral deposits; John Wiley and Sons, Inc., New
York, 916 p.
Emmons, W. H., 1938, Gold deposbts of the world; McGraw Hill, New York, 562 p.
Granger, A. E, Mendell, M. G., Simmons, G. C., and Lee, Florance, 1957, Geology
and mineral resources of Elko County, Nevada; Nevada Bureau of Mines Bull. 54,
190 p.
HIII, J. M., 1916, Notes on some mining d~str~cts in eastern Nevada; U S. Geol. Survey
Bull. 648, p. 88-95.
Johannsen, Albert, 1931, A descriptive petrography of the igneous rocks, vols. 1-11];
Univ. Chicago Press, Chicago, Ill., 1506 p.
King, Clarence, 1878, United States geological exploration of the fortieth parallel,
vols. 1-11; Government Printing Office, Wash~ngton, D C., 1693 p.
Pabst, Adolf, 1928. Observations on inclusions In the gran~t~c rocks of the Sierra
Nevada; Univ. Calif. Pub., Bull. Dept Geol. Sci, vol. 17, No. 10, p. 325-386.
Ramberg, Hans, 1952, The origin of metamorph~c and metaso~nat~c rocks; Univ. Chicago
Press, Chicago, Ill., 317 p.
Ross, C. S , and Smith, R. L , 1961, Ash-flow tuffs: their orig~n, geologic relations
and identification; U.S. Geol. Survey Prof. Paper 336, 80 p.
Stringham, B. F., 1957, Geology of the Kingsley quartz monzonite stock, Antelope
Range. Eastern Nevada (Abs.); Geol. Soc. Amer. Bull.. vol. 68, No. 12, Pt. 2, p.
1873.
---- , 1958, Relationsh~p of ore to porphyry in the Basin and Range Province,
U.S.A.; Econ. Geol., vol. 53, No. 7, p. 806-822.
Turner, F J., and Verhoogen, J., 1960, Igneous and metamorphic petrology, McGraw-
Hill Book Co., Inc., New York, 694 p.
Manuscript rece~ved May 23, 1966

A Study of Fluid Migration in Porous Media
by Stereoscopic Radiographic Techniques*
J. RAYMOND RUTLEDGE
Phillips Petroleum Company
ABSTRACT.-Stereoscopic radiography provides an effective method of studying small-scale
fluid migration in porous medlia in that it permits visual observation in three dimen-
sions of the fluid front and its relation to sedimentary structures. The technique con-
sists of imbibing or forcing an opaque radiographic solution into a rock specimen from
a centralized point source while procuring a series of stereo paired radiographs. The
thickness of sample in which this process can be adequately viewed by radiography is
limited to about three centimeters.
Viswlly obscure "cryptostmctures" commonly develop pronounced control on fluid
movement. Thirty percent of all the homogeneous sandstones used in this study de-
veloped anisotropic flow patterns resulting from such structures. This represented,
however, controlled flow patterns in 80 percent of the homogeneous samples in which
cryptostruaures had been detected by radiagraphy. In contrast, little or no control was
effected by cryptostruaures in 22 percent of all the sandstone samples including both
visibly stratified and homogeneous types. It is concluded that cryptostmctures, like
visible structures, affect fluid movement only to the extent that they represent aggregate
differences in effective porosity. In seemingly homogeneous sandstones they may reduce
or even prevent fluid transmission.
CONTENTS
TEXT
page
Introduction ......................................... 90
Scope and - purpose - ............................ 90
Previous work ................................ 90
Acknowledgments ................................ 91
Procedures and Techniques ................ 91
Experimental equipment ................ 91
Fluids ................................................ 92
ILLUSTRATIONS
Text-f igure Page
1. Experimental apparatus ............ 93
- ,.
1 able
1. Visual and radiographic
comparisons of samples ............ 95
Plates
1. Fluid flow patterns .... after page 96
Sample preparation .......................... 92
Imbibition and injection
procedures .................................... 93
2.
3.
Miscellaneous patterns
.................................... after page 96
Cryptostructural control in the
Radiographic techniques .................. 94 Illipah Sandstone .... after page 96
Nature and Distribution 4. Cryptostructural control in a
of Samples .................................... 94 Tertiary Sandstone from the
Cryptostructures Revealed Ventura Basin ........ after page 96
by Radiography ............................ 94 5. Structural control in the
Fluid Front Patterns in a Variety Berea Sandstone .... before page 97
of Sandstones ................................ 98 6. Ineffective structures in visibly
Effects of Cryptostructures on stratified Weber Sandstone
Fluid Flow .................................... 99 ................................ before page 97
Observations of Fluid Patterns 7. Ineffective structures in seem-
in Prewetted Samples ................ 102 ingly homogeneous Frontier
Comparison of Flood Front Sandstone ................ before page 97
Patterns to Fabric ........................ 102 8. Controlled pattern in the
Conclusions .......................................... 102 Englevale Sandstone Member
Sample Localities .................................. 102 of the Labette Shale
References Cited .................................. 103 ................................ before page 97
*A thesis submitted to the faculty of the Department of Geology, Brigham Young Uni-
versity, in partial fulfillment of the requirements for the degree Master of Science, July
28, 1966.

J. RAYMOND RUTLEDGE
INTRODUCTION
Purpose and Scope of Study
Fluid migration has been extensively studied and most physical properties
of porous materials and percolating fluids have been analysed o'r mathemtically
pred~icted. Allthough 'the nature of the fluid fronts has been studied in varlous
ways, it is difficult to v~sually analyze thls phenomena In three dimensions
especially In naturally llthifled sedimenlts. Most of our present knowledge is
'the resul't of indirect observations oa artificial materials Flow patterns In 11thihed
sediments, however, commonly defy theoretical predictions because of
i,ncidental ~rregular~t~es in sorting, cementing, fabric, and sedimentary structures.
Hamblin (1965) recently demonstrated that s'tructures commonly exlst in
bhe majority of seemingly homogeneous sandstones. Such features provlde a
plosslble explanatimon to anisotropic fluid migrsti,on and unexpected configurabion
of fluld interfaces especially In khe hcntogenmus type sandstones. The
purpose of thls ytudy is t.0 evaluate such pssi,b~l~ties. The flrst cons~deration
was to explore the use d stermcoplc rad'iography as a means of wisually
analyz~ng the ccnfiguration of an advancing flutid front in three drmensions.
Inasmuch as sedlmentary structures, whether hldden or visi'ble, are readlily detected
~18th rad~ography, both the locatieon of such features and the development
of the fluid front can be related. A prel~minary evaluation of the effect
of cryptostructures on fluid flow was therefore a second consideration in this
study.
Prevlous Work
Basic principles governing fluid flow condltlons and rates were no:ably
advanced by the early work of King (1899) and Sl~chter (1899). The an'alytlc-
a1 and mathematical treatments of fluid motion and reservoir properties were ex-
ttensively added to by Muskat (1937). Hubbert (1940) developed an advanced
theory of fluid flow whih related thermodynamlc principles for the flrs't time.
Meinzer and Wenzel (1942) extended knowledge of the relations~h~ps between
permeabils~.ty, hydraullic pressures and reservoir storage. Most of these contributions
were advanced In the areas of hydrology. Subsequent contrlbut~ons resuliblng
from an expl~os~ve interest In this area by the petroleum, hydrology,
and engineenng ~ndusknes are too numerous to ment~on. Scheidegger (1960)
produced an rmportan't compilation of the dynamlc, chemical, and mathematical
relationslh~ps whlch have been establ~shed and has also made frequent contrlbuelons
in- the same frelds.
Stud'ies relatrng porosity and permeability to the structural framework of
porous medla are comparatively few. Newell (clted by Klng, 1899, p 126)
and Fettke (1938) noted bhe anisotrop~c character of perrneabil~t~ in sandstones
Correlmations between grain packlng, poroslilty and permeabils~ty were studied by
Fraser (1935) and Cotton and Fraser (1935). Grlffi,ths (1949) and Grlffiths
and Rosenfeld (1953) lnvestlga'ted the relatlon between fabrlc 2nd veLcbr~al
permeaibility. Others who explored fabric and permeabll'ity relatlonshlps Include
Hubta (1956) and Potter and Mast (1963). They were unable to esta.bli,sh any
strong relationshmips between the orientahon of dimensional fabrlc and maximlum
permeability. Lrhr (1961) conducted one of the few experiments ubiliz~ng
consolid~a.ted materials to compare flow patterns wlth graln-size dlstributinn
The rnicrcscopic study of fluid phenomena in an art~ficial systelm by Chatenever

RADIOGRAPHIC TECHNIQUES IN FLUID MIGRATION 91
(1951) provided a demonstrabion of basic fluid frcnt patterns produced when
an immiscible fluid invades a prewetted system.
X-ray techniques obillized by Laird and Putnam (1951) enabled them to
~nstrumenbally deduce the extent of fluid saturab~on in a porous sample. Hamb-
lin (1962, 1965) extended the use of radiography to study the internal nature
of sandstones and also demonstrated the extensive occurrences of structures in
seemingly homogeneous units.
ACKNOWLEDGMENTS
Thmis investigabion is part of a more extensive project exploring bhe use of
radiographic techniques for geologic studies. It was largely supported by the
National Science Foundsabion rhmugh grant GP-1980, to Dr. William Ken-
ndh H,amblin.
The author wishes to express grateful appreciakion to Dr. Wrn. Kennetth
Hamblin who suggested this problem, provided constant suggestions and super-
vision, and offered constructive criticimsm of the manuscript. Dr. Harold J.
&issell collected and idendfiied many sandstones used in this study and offered
many importaat suggegbions. The assivtance and encouragement of my wife,
Kaye, is al'so sincerely appreciated.
PROCEDURES AND TECHNIQUES
Stereoradiography util~izes h e same basic principle of procuring a stereo
scopic image as stereo photography. The major di'fference, however, is that radi-
ography mtilizes the abuorben,t contrasts of d,i,fferent chemical and mineral
composikions to produce a relntzble, internal imlage on the film. Such a mehod
enables one to look ink0 a rock as if ict were transparent, viewing in effect the
positions and structural relationships of the various constituenlts in three di-
mensions. If fluids, which are opaque to x-mays, are injected or imbibed into
a specimen the configurabion of bhe fluid front inside the rock will also be
seen. By making a series of stereoscopic x-ray pictures a progressive record of
fluid emplacement and advance can be preserved and studied. The radiographic
fluids, as well as the highly absorbent m,inerals like m~agn&ite, hematite, biotite,
zircon, and calcite, will appear as dark images on the psistive prin'ts taken from
the radiographs.
Experimental Equipment
Equipment used in experimental work consi,sted of an x-ray unit, an exposure
box, and a fluid pressure system as illustrated in text-figure 1. The x-ray unit
was of a medical type rated with a 150 kilovoltage (KvP), 200 milliamp (Ma)
potential. R,apid exposures used in procuring time-lapse sequences commonly
necessi'tated khe use of the "hard" type x-my exposures. When much softer
radiation was desirable, a smaller industrial unit with a beryllium window was
employed. Kodak indusltrial film types "M" and "R" were utilized because d
heir h,igh con~trast and fine grained quali~ies. To econom~ically facilitate rapid
time-lapse exposures of injection and irnbilbitlion patlterns in verkically positioned
samples, a lead-lined exposure box was constructed to permit approximately
one-eigh~th of an 8x10 film sheet to be exposed at a time while the other part
was pmtected from exposure.
Pressurized fluid injections were conducted with the use of a modified
hydraulic brake-bleeder tank marketed by K-D Tool Company. A 2-60 psi.

92 J. RAYMOND RUTLEDGE
pressure gauge and a md~ified rapid-coupling hose system were added to the
basic unit. The hose system of the fluid tank was secured by a screw type clamp
to the bases of standard mcd,iaal hypdermic needles used to conduct rhe fluid
to the center of the sample. Needles wlth interior diameters of 0.7 to 0.9 mrn.
(sizes 14 to 18) provi'ded devlrable resu1.t~.
Several hlghly absorbenlt or opaque radiographic flu'ids were found to be
useful in delimiking interconnected pore sysltems during ~njention and gravity
flow procedures. They included:
(a) "Dltriokon"-an angiocardiograph~c solutlon formed from sodlum
dlprotirizoate and distrimate and produced by Mallinckrodt Inc.
This medium is extremely opaque to x-rays and produces an excellent
conltrast on radiographs. Its low viscosity (45s~ at 76 F.) and h~gh
contrast made it the most useful of the fluids for thls study.
(b) "Baridol"-a commercially prepared opaque medium containing
colloidally stabilized barium sulphate. Th,its product is marketed by
Pac~f~c Chemicals. Because of its high viscosifty (621ssu at 76 F.), moderately
high con'tr& and low cost it was found to be most useful for
imbi,bi,tion tests on poorly indurated sandstones.
(c) Sodium Iodide solutron-a mixture of 40 gms. of sod!ium iodide
(U.B.P.) to 100 ml. water was found to produce contrasts sufficient to
be used in rnoder~tely indurated sandstones. This concentration provided
only fair contrasts, a near maximum for the solution, and a very low
viscosity (28ssu at 78.6 F.).
(d j Mixtures-mixtures of Barldol and NaI solution (as above) en-
hanced the desirable prope~ties of each--low viscosity and moderate to
high contpasks. Three mixtures were used : (1) 15% Barldol, 85% NaI;
(2) 30% Baridol, 70% NaI; and (3) 50% Bsaridol, 50% NaI.
(e) Potassium Iodide wlu~ion-a mixed solution wi~h similar properties
as NaI solution.
There are many other g d radiocardiographic solutions on the market
which could have been used but generally their costs were pmhibitive to th~s
type of study.
Sample Preparation
Rock samples were sl:iced Into rectangular specimens which would fit into
the window of bhe exposure box. The thickness of each specimen type vapid
according b its apparent degree of induration and permeability; the more
poorly indurated, highly porous sandstones being cut hick&. The most useful
range of thickness vaned between one and three centimeters. Specirnenls were
generally sliced perpendicuhar to bhe apparent stratification planes and or~ented
so that these planes would be situated in a horizontal position during lnjec-
tlons or gravity flow. Each sample was also dried in an attempt to remove
interstitial fluids. The maln requirement, aslde from limiting thicknesses, was
the necessity of havlng samples void of open fissures.

RADIOGRAPHIC TECHNIQUES 1N FLUID MIGRATION 93
Needle
Pressure
&
Regulator . . I,: ._ \Ill/
. .. : '!!!I
.. . .
! ! X-Ray
Fluid System . . . . . .
Specimen Tube
1 EXT-FIGURE 1 .-Experimental Apparatus
(A) Injection System
(B) Exposure System
B.
TOP VIEW
Samples were t'hen prepared for vapious fluid flow experiments whlich in-
oluded both irhhitian, and injeion of dry and prewetted systems. The more
f~iable sandstone types were prepared for imbibition tests by simply djrilling
an open hole or "well" about half way bhrough the cut specimens with a one
cenbimeter diameter masonry bit. The remaining sandstone types had much
smaller holes drilled inho them to accomodate the hypodermic needles used
for injtwtions. Hot Canadian balsam was then used to seal the needles in place.
Special efforts were made to prevent clogging of rhe pore openings in bhe
immedimate vicinity of the needle bip and b seal all other areas of the dri~lled
hole. The desired effect was to provide a centralized pint-source for the
injected fluids. Prewetted systems were additionally prepared either by soaking
the specimens in kerosene for several days prior to being injected or by pre-
injecting the specimen with a light-comtrast med'ium, then conducting the
expeaiment with a high-contrast med,ium. Occasionally flow conditions of both
system's were controlled by sealing certain sides af the specimens wisth wax.
Selected samples, which had previously been injected and which had de-
veloped patterns seemingly little af fected by their inherent structural features,
were cut into four or five wafer-thin sl~ices and x-rayed with rhe soft rays of
the industrial unit in an effort to detect grain fabric and to determine its rela-
tion with the emplaced opaque media.
Imbibition and Injection Procedures
hth continuous and periodic imbibition and injection procedures were used
depending on the type of radiograph,ic record desired. True time-lapse sequences
were possi'ble only when single radiographs were hken but when stereo paired
radiographs (stereoradiographs) were desired a staggered series of exposures
were made. This involved releasing fluid pressures for periods of one to four
minutes in order to prevent vokurne changes in the fluid front between exp-
ures of the stereo pairs and to allow the x-ray cathode to cool. Comparisons
made between patterns developed under conltinuous and period,ic injections in
the same sandstone had so little variance that the methods were considered
comparable for this study. The Frontier Sandstone provided a partial exception

94 J. RAYMOND RUTLEDGE
to the normal. Both pressures and the types of fluids used depznded upon
the compactness of the sand'stone samples. Generally, pressures had to be increased
in steps as the fluid front expanded farther from the po. ~nt source.
These increases were inriltiated when it became apparent that the fluid front
b d stabilized as a resulmt of surface attraction and other fluid interactions.
OcGasionally a single pressure plateau was all that was necessary during a
complete injedtion.
The more viscous fluids used in imbibition runs were conducted into the
werbl from a separation funnel wi~th a regulatory 3topcock. Imb8ibi'tions were likewise
continuous when single radiographs were taken and periodic when stereoradliographs
were desired. Longer time intervals were needed to prevent movment
between exposures as a resul't of increased capillary action.
Radiographic Techniques
Radliographs were taken on the medical unit from a 26 inch focal-film
distance. Exposures on this unilt were commonly made using the small 1.0 mm.
focal spot at 60 KvP and 100 Ma. Stereoradmiographs were produced by shifting
the x-ray tube verbically a total of 7.6 cm. and inclining it toward the
specimen about fcur degrees from the horizontal in both top and bottom positions.
The stereoshift was made perpendicular iw the ~tratifica~tion planes so as
to increase the possibili.ties of aligning the emitted x-rays parallel to internal
structural planes thereby increasing possible density contrasts on the x-ray film
denoted by such struotures. Tilting the x-ray tube is reported to enhance the
stereo im'age. Films were processed in Kodak developer and fixer. For a more
concise treatment of various radiographic techniques and principles cne should
refer to publications by Clauser, 1952, p. 65-10>; Eastman-Kodak, 1957; or
Hamblin and Salotti, 1964, p. 19-21.
NATURE AND DISTRIBUTION OF SAMPLES
The 44 sandstone b~mples utilized in this study were obtained from 35
formations representing a wide variety cf sedimentary types and environments,
ages and post-depositional conditions. They include samples from nine states
located chmiefly in the Midcontinent, Colorado Plateau and Great Basin areas.
As b&h bhe presence and the apparenlt absence cf visually detectable internal
structures were imp0fitan.t considerations in this study, equally representative
groups of such types were included in the sands'tones selected. Radiographs
revealed the true extent to which the apparently homogeneous sandstones were
void of sltructures and commonly enhanced deltails of visible structures. A ccm-
parison of the resulting differences is included in Table 1.
It should be noted that the term "sandstone" is herein used only with a
grain size connotation ccncurrent with the Wentworth scale. Also the sand-
stones used in this study represent bclth selective and random choices and any
inferred results extend'ing outside bhe area of this study have limited merit.
CRYPTOSTRUCTURES REVEALED BY RADIOGRAPHY
Visual examination of the sandstone surfaces revealed that one-half were
void of any evidences of stratification. Very thin bedded units (1 to 5 cm.)
and laminations (less than 1 cm.) were prominently or vaguely suggested in
about two-thirds of the other samples and cross-laminations and cross-bedding,

Internal features
RADIOGRAPHIC TECHNIQUES IN FLUID MIGRATION 9 5
TABLE 1
Visual and radiographic comparisons of samples
Homogeneous* 2 2 50.0
Laminated or bedded 16 36.3
Cross-lammated or cross-bedded 4 9.1
Both lammated and
cross-lammated 0 0.0
Graded bedding 1 2.3
Disturbed bedding I 2.3
*Complete absence of any distinct or obscure stratification
**All samples contamed other strat~fication
Visual appearance Radiograph appearance
No. samples 9% samples No. samples % samples
graded bedding and disturbed or reworked features were evlden,t in the remainder.
A conclse breakdown of these figures can be noted in Table 1.
Rad~iographs exposed hidden internal structures, referred to as cryptostructures,
in 37 percent of the seemingly homogeneous unlts and considerably
enhanced the vague details o'f visual structures in many other samples. In most
cases these structures consisted of such bas,lc primary features as del' lcate crosslamlnae
and horizontal lamlnae occurring alone or in various combinations The
structural framework of visually s~tratlfled units was somet~imes strikingly dlfferent
than expressed to the naked eye. Freshly cut surfaces of a cored sample
of the Berea Sandstone from central Illinois, for example, displayed prominent
RADIOGRAPHS OF FLUID FRONT PATTERNS IN A
VARIETY OF SANDSTONES
FIG. 1.-Smooth, ~sotroplc front ln seemingly homogeneous Weber Sandstone from local-
~ty (10). Spec~men thickness 17 cm., cumulative ~njection 7 mln. at 10 psi., fluid
D~triokon. Exposure at 60 Kv, 100 Ma for 10 secs. xl.
FIG. 2.-F~nger~ng or dendr~t~c front in seemingly homogeneous Englwale Sandstone
Member from locality (3). Specimen thickness 1 5 cnl.; cumulat~ve injection 16
min. at 5 psi.; fluid D~tr~okon Sample prewetted with Kerosene. Exposure at 60
Kv, 100 Ma for 9.5 sec. xl.
FIG. 3.-Lobate front in well lammated Tonganoxie Sandstone from local~ty (7). Specl-
men th~ckness 1 3 cm., cumulative Injectlon 5 mln at 4 ps,i.. flu~d D~tr~okon.
Sample waxed. Exposure 50 Kv, 100 Ma for 12 sec xl.
FIG. 4 -Tongued front ln cross-bedded Dakota Sandstone from local~ty (4). Specimen
thickness 2.8 cm., cumulative ~mb~bition 6 mln., fluid 50'7;
solution Exposure at 60 Kv, 100 Ma for 12.5 sec xl
Bar~dol, 50% NaI
FIG. 5.-Lateral front ~n highly laminated Cretaceous sandstone from local~ty (8). Con-
tams shaly partings. Specmen thickness 1.5 cm.; cumulat~ve injection 7 min. at 20

96 J. RAYMOND RUTLXDGE
psi + 30 min. at 30 psi + 30 min. at 40 psi + 5 min. at 50 psi; fluid Ditriokon
Exposure 60 Kv, 100 Ma for 10 sec. xl.
FIG. 6.-Irregular front in homogeneous Baseline Sandstone from locality (1). Speci-
men thrckness 3.2 cm ; cumulative rmbibition 46 mln.; fluid Bandol. Exposure 70
Kv, 100 Ma for 1 1 sec. xl.
EXPLANATION OF PLATE 2
MISCELLANEOUS FLUID FLOW PATTERNS
FIG. 1.-Photograph of "isochromatic absorbtion rings" formed on surface of Frontier
Sandstone from locality (5). Dark rings are wetted by injected fluids, light colored
rings are dry surfaces. x1.3.
FIG. 2.-Radiograph of a d~ffused lobate front formed In prewetted specimen of Tonganoxie
Sandstone from locality (7). Compare w~th "dry" specimen of figure 3,
plate 1. Specimen thickness 2 cm.; cumulative Injection 3 mrn at approximately 8
PSI.; flu~d Ditr~okon. Exposure 80 Kv, 85 Ma, 4 secs. xl.
FIG. 3.-Radiograph of secondary tongued front formed in preimbibed specimen of
Dakota Sandstone from locality (4). Compare w~th exposure of preceding imbibition
Plate 1, (fig. 4). Cumulat~ve ~mblbrt~on (secondary only) 3 min.; flurd
Ditriokon. Exposure 60 Kv, 100 Ma, 12.5 secs. XI.
STEREORADIOGRAPHS OF A CONTROLLED FLUID FRONT IN A
HOMOGEXEOUS SAMPLE OF ILLIPAH SANDSTONE FROM
HAMILTON, NEVADA
General explanation-shortened sequence of exposures revealing cryptostructural control
of injected fluid. All exposures made at 60 Kv, 100 Ma for 7 secs. Specimen thickness
1.7 cm, fluld D~triokon. Specimen Injected from uprlght position with needle end at top.
FIG. 1.-Flu~d pattern after cumulative injection of 7 mln. at 3 psi. + 3 mln. at 5 psi.
FIG. 2.-Fluid pattern after curnulat~ve Injection of 7 min. at 3 psi. + 7 min. at 5 psi.
FIG. 3.-Fluid pattern after cumulative injection of 7 min. at 3 PSI. + 14 min. at 5
psi. + 7 min. at 10 psi.
FIG. 4.-Flurd pattern after curnulatlve ~njection of 7 min. at 3 psi. + 14 min. at 5 psi.
+ 13 min. at 10 psi.
STEREORADIOGRAPHS OF A CONTROLLED FLUID FRONT
IN A HOMOGENEOUS TERTIARY UNIT CORED IN THE VENTURA BASIN
General explanation-shortened sequence of exposures revealing moderate cryptostmdural
control of injected fluid. All exposures made at 60 Kv, 100 Ma for 10 sec. Speclmen
thickness 1.5 cm.; fluid Ditriokon. Specimen injected from upright position with needle
end at top.
FIG. 1.-Fluid pattern after cumulative injection of 4 min. at 10 psi.
FIG. 2.-Fluid pattern after cumulative Injection of 4 min. at 10 psi. + 3 min. at 15 psi.
FIG. 3.-Fluid pattern after cumulative injection of 4 mrn. at 10 psi. + 9 min. at 15
psi. + 3 min. at 20 psi.
FIG. 4.-Fluid pattern after cumulative injection of 4 min. at 10 psi + 9 mln. at 15
psi. + 9 min. at 20 psi.

RUTLEDGE
MF6
FLUID FRONTS IN VARIOUS SANDSTONES
-
PLATE 1

PLATE 2 RUTLEDGE
2 3
MISCELLANEOUS FLUID FLOW PATERNS

RUTLEDGE PLATE 3
I"'
4
FLUID FRONTS IN ILLIPAH SANDSTONE

PLATE 4 RUTLEDGE
4.
FLUID FRONTS IN HOMOGENEOUS TERTIARY SANDSTONE

PLATE 6 RUTLEDGE
4
FLUID FRONTS IN WEBER SANDSTONE

RUTLEDGE PLATE 7
4 8
FLUID FRONTS IN FRONTIER SANDSTONE

PLATE 8 RUTLEDGE
-
a m *
FLUID FRONTS IN ENGLEVALE SANDSTONE

RADIOGRAPHIC TECHNIQUES IN FLUID MIGRATION
STEREORADIOGRAPHS OF CRYPTOSTRUCTURAL CONTROL IN A
STRATIFIED CORE OF BEREA SANDSTONE FROM ILLINOIS
General explanation--shortened sequence of exposures revealing unexpressed cross-stratifi-
cation and structural influence on fluid migration. All exposures made at 45 Kv, 100 Ma
for 20 sec. Specimen thickness 1.3 cm., fluid Ditriokon. Specimen injected from upright
position with needle at top. xl.
FIG. 1.-Fluid pattern after cumulative injection of 3 min. at 15 psi. + 3 min. at 20 psi.
FIG. 2.-Fluid pattern after cumulative injection of 3 min. at 15 psi. + 7 min. at 20 psi.
FIG. 3.-Fluid pattern after cumulative injection of 3 min. at 15 psi. + 12 min. at 20 psi.
FIG. 4.-Fluid pattern after cumulative injection of 3 min. at 15 psi. + 18 min. at 20 psi.
STEREORADIOGRAPHS OF INEFFECTIVE STRUCTURAL CONTROL OF
FLUID MOVEMENT IN A STRATIFIED SAMPLE OF WEBER SANDSTONE
FROM BLUE MOUNTAIN. COLORADO
General explanation-shortened sequence of exposures revealing- seemingly isotropic
permeability in a visibly stratified sandstone. All exposures made at 60 Kv, 100 Ma for
9 secs. Specimen thickness 1.8 cm; fluid Ditniokon. Specimen injected from upright
position with needle end at top. xl.
FIG. 1.-Fluid pattern after cumulative injection of 1 min. at 5 psi.
FIG. 2.-Fluid pattern after cumulative injection of 4 min. at 5 psi.
FIG. 3.-Fluid pattern after cumulative injection of 10 min. at 5 psi. + 1 min. at 10 psi.
FIG. 4.-Fluid pattern after cumulative injection of 10 min. at 5 psi + 2 min. at 10
psi + 1 min. at 20 psi. Sample waxed on front and back surfaces just prior to
making 1 min. injection at 20 psi.
RADIOGRAPHS OF INEFFECTIVE STRUCTURAL CONTROL OF
FLUID MOVEMENT IN A HOMOGENEOUS SAMPLE OF FRONTIER
SAKDSTONE FROM THE VICINITY OF VERNAL, UTAH
General explanation-condensed sequence of exposures revealing isotropic fluid flow
across laminated cryptostructures. All exposures made at 60 Kv, 100 Ma for 8 sec.
Specimen thickness 1.8 cm, fluid Ditriokon. Specimen injected from upright position
with needle end at top. xl.
FIGS. 1-3.-Fluid pattern after cumulative injections of 1, 3, and 6 min. at 5 psi.
FIG. 4.-Fluid pattern after cumulative injection of 9 min. at 5 psi. + 2 min. at 15 psi.
FIG. 5.-Fluid pattern after cumulative injection of 9 min. at 5 psi. + 7 min. at 15
psi. + 5 min. at 25 psi.
FIG. 6.-Fluid pattern after cumulative injection of 9 min. at 5 psi. + 7 min. at 15
psi. + 15 min. at 25 psi.
FIG. 7.-Fluid pattern after cumulative injection of 9 min. at 5 psi. + 7 min. at 15
psi. + 20 min. at 25 psi. + 5 min. at 30 psi.
FIG. 8.-Fluid pattern after cumulative injection of 9 min. at 5 psi. + 7 min. at 15 psi.
+ 20 min. at 25 psi. + 30 min. at 30 psi.

98 J. RAYMOND RUTLEDGE
STEREORADIOGRAPHS OF OBSCURE STRUCTURAL CONTROL OF FLUID
MOVEMENT IN THE ENGLEVALE SANDSTONE MEMBER OF THE
LABEITE SHALE OF EAST KANSAS
General explanation-shortened sequence of an obscurely controlled anisotropic pattern
advancing along a fingening front. All exposures made at 60 Kv, 100 Ma for 10 secs.
Specimen thickness 1.5 cm; fluid Ditriokon. Specimen injected from upright position
with needle at top. XI.
FIG. I.-Fluid pattern after cumulative injection of 1 min. at 5 psi
FIG. 2.-Fluid pattern after cumulative injection of 5 rnin. at 5 psi. + 1 min. at 10 psi.
FIG. 3.-Fluid pattern after cumulative injection of 5 rnin. at 5 psi. 3- 7 min. at 10 psi.
FIG. 4.-Fluid pattern after cumulative injection of 5 min. at 5 psi. + 27 min. at 10 psi.
horizontal planes 0.5 to 4 cm. apart; however, when x-rayed, a profusion of
deiicate micro-cross-lam,inobions was eviden~t-comprising in effect the dominant
type of internal feature present in the ~tructural framework of the specimen.
1.t is commonly known that rhe expression of stratification is a result of
prominent depsijtional changes in texture, composition, cementation or pc~simbly
fabric and that it is often enhanced by post-depositional conditions such as
dliagenesis, differential weathering, and oxidation. When, however, primary
struotural units are delim,ited by surfaces constain'ing concentrat.ions of accessory
minerals, sim,ilar in color and texture to the surrounding grains or even by
differently colored accessory minerals sparcely distributed along the interfaces,
stratification will seldom be detecte'd by the eye. On the other hand, any subtle
variations in the forementioned propepties will resubt in densi'ty differences
read,ily detected by rad'iographic methods. These density differences, ho~wever,
are rapidly modified or reduced as increasingly thicker samples are used and
when the inherent structural planes are oriented toward a pition perpendicular
tu the x-rays.
FLUID FRONT PATTERNS IN A VARIETY OF SANDSTONES
As the radiographic contrast solutions were injected and imbibed into the
sand,stone samples, zones and channel-networks of greatest permeability were
dlishinctly outlined on the radiograph sequences. The degree to which the samples
were anisotropic were reflected in the spherical, el1,iptical or irregular configurations
of the emplaced fluid interfaces. Homogeneous sands characterisbicdy
develop basic isotropic or spherical forms such as illustrated in figure 1,
Plate 1. Sands wirth a preferred direction of permebilfity developed an eccentric
anisotropic form (see Plate 3), and sands reflecting inhomogeneous condifbions
developed an irregular form (see Plate 1, fig. 6).
The advances of t,he f'ld front e~tremi~kies in the basic forms were characterized
by a variety omf fronts. Four types of fluid fmn.ts were recognized and
are illuukra.ted on Plate 1. They are herein referred to as:

RADIOGRAPHIC TECHNIQUES IN FLUID MIGRATION 99
(1) Smooth front-a sharply defiined front which develops in sand-
stones in whfich cementing materials are of relatively liwle importance;
pore systems are dependent on grain packing and seemingly intercon-
nect around every grain. They are most commonly developed in homo-
geneous uni'ts. A typical example of bhi,s front is illuutrajted in a mas-
sive sample of the Weber kndwtone (Plate 1, fig. 1).
(2) Fingering or dend~ibic front-a branching front whlch advances
along a selective network of hairlike channels because of signiflcant
amounts of cementing material betwee'n grains and because of increased
cap~llary act~on. This type of front was noted with various degrees
of prominence in all but the well-stratified sandstones used in this
ytudy. Dendrit~c fronts appear to be the most basic form of frontal advance;
however, they are seldom developed sufficiently to be noted apart
from the smooth type of fron't. Well developed examples of this front
formed ln samples of the Englevale Sandstone Member of the Labette
Shsale of east Kansas (Plate 1, fig. 2).
(3) Lobate, tongued, and lateral fronts-types of lobed, wedged and
elongated fronts whlich derive their dmistinct forms from zones of differing
permeabili'ty mincidenlt w'ith stratification. Mate forms were
most common to well-laminated units and tongued fronts to cross
dratified units. Sandstones possesui7ng shale-like m~crolaminations or
except~onally variable porosity normal to bedding planes, such as in
graded turbidite sands, developed highly restricted flow zones. Examples
of these types are noted in Plate 1, figures 3, 4, and 5.
(4) Irregular front-fronts exhibitting extensive abnormalities re-
flecting eimther inhomogeniety or minute structures which were not de-
tected by the type of rad.iabion used (Plate 1, fig. 6).
Extraneous patterns were repeatedly developed in two relatively homogeneous
sandstone types. Plate 2, figure 1 is a photo of the surface appearance
of one such pattern on the Fronbier Sandstone. The darker rings are wet surfxes
and the l~ghter ones dry surfaces. X-rays reveal the con'tinuation of these
ring-like structures within the sample, often in greater numbers than expressed
on the exterior surface. The number of rings appears to coincide w~fh the
number of ~nterm~btent injections that were introduced. Thfis 1s borne out by
the fact that such rings did not form duging continuous injection procedures.
fist rings formed on the back surface of the sample which was in contact
with the film plate during injections and exposures, but vari,abions showing m e
rings on the fron't surface and tthe remainder on the back were also noted. Ir
has been tentatively suggested that his phenomenon represents isochromatic
absorption resulting from a reaction been the clay and silt constituen'ts and
the fbid. Verifictikion of such a suggestion was not pursued as these incidents
represenlted only anomalous sidelights to the in'tent of this study.
EFFECTS OF CRYPTOSTRUCTURES ON FLUID FLOW
Flow conditions were prd,uced in 34 of the 44 sandstone samples by
utill~izing pressures un,der 58 psi. The remainder of samples were impervious to
fluid movement under the Ilmitations of these conditions. Flood front advances
in prn~able samples were variously affected by structural interfaces; in some a

100 J. RAYMOND RUTLEDGE
strong con~t;rollr,ng influence was noted while In others the complete lack of such
influence was inversely evident. About two-th~rds of the samples were rerun,
some as many as five times, in order to ensure the repeatab'ilrty of the phenomen~a
observed.
The results of observations made on seemingly homogeneous sandstones
containlimng cryptostructures proved most interesting. Out of five samples ava1.1able
for fluid flow tests, four of them developed flood front patterns reflecting
control by cryptostructures. The massive Illi'pah Sandstone (Plate 3) 1s an
example which exhibtts a strong degree of control. One notes in this shoatend
sequence of pictures how the axis of elongation of the flooding front al~gns
itself parallel to the poorly developed stratification. Incl~natlon of the anisotrop~c
IC axis noted In the last radiograph of the sequence may posv~bly reflect an
Inherent im,bricated fabric wh,ich became more evldent under slow capillary
movement. The extrem~ties of the anisotro~ic form are also seen to advance in
1
a weak fingering manner. The more prominent frontal edge of the bottom
photo resulted from crystalliza~tion of the fluid which remalned In the sample
overnight prior to taking the last radiographs.
Plate four illustrates moderate cryptcstructural control on a f~ne-gra~ned,
homogeneous Tertiary sand cored In the Ventura Basin. The faint discont,inuous
1,aminae revealed by x-rays are undoubtedly responsible for the Iobate fo~m developed by the fluid as matchlng indentat~ons on either s~de of the pattern
parallel the laminae. Encroachment of fluid across cerbain of the lm~nae IS, of
course, retarded by reduced permeabil'ity. A more controlled front would undoubtedly
have resulted if the laminae had been more continuous. Note also
bhe smooth front which is conbinuously expressed.
The results of relatable, observable cofitrol in a calculated 30 percent of all
the homogeneous sandstones in these experiments are significant. Many massive
appearing sandvtones wilth good porosity may fail to be good aquifers or reservoirs
for this reason rather than erratic cement distr~bution, et cetera.
It is also noted that similar occurrences of f l d front cont'rol by unexpressed
cryptmbrudures are evident, though to a lesser degree, in sandstones which
express only a part of their stratlf~ication to bhe eye. Laminar planes viewed on
he cut surfaces of a cored sect~on of Berea Sandstone for example, are delicately
diupLayed on radiographs as highsly developed micro-cross-laminations interbedded
wibh less prominen~t horizontal microlaminations (Plate 5). Upon injdion,
a degree of struotural control by even the more del~cate structures is
mbiced. Hair-like extensions of the flood front are seen to favor a planar
oaientation parallel to structures. Note also how the thin threads of fluid curl
over to parallel the laminae on bhe lef't side in the vicinrty of the needle In
laater exposures. Most rapid advances of he fluid faont occur along particular
structural interfaces in bhe micro-cross-lam~nated sectlon and a tmrt~on of the
microlaminated sect~on as can be nolted particularly in the top stereo pairs. The
front continuously reveals a notable parallelism w~th the m~crolam~nations of
the left side while on the right side and bottom it abuts against a near impervious
barrier formed by he interface of one of the micro-cross-lam~nae. In
effe~t the nestled form developed by the emplaced fluid would hardly be expected
if one were to approximate the configuration of such a front by considering
onlv the visible laminae.
0;the Ather hand, both hidden and visible structures were noted to impart
little or no effect upon advancing flood fronts in a number of other samples

RADIOGRAPHIC TECHNIQUES IN FLUID MIGRATION 1101
In these cases flood fronts developed essenltially spherical, isotropic-like forms.
Such occurrences were noted in 23 perrenlt of the visibly stratified sandstones
and 20 percient of the cryptostructured "homogeneous" unik. A promlinently
strat~fied hand sample of Weber Sandstone, for example, developed little
struotural control on the fluid front unltil late in the sequence (see Plate 6). A
spherical form is mainhained by the front while crossing a number of horrzontal
laminae. Upon reaching the upper cross-laminated unit increased permeability
results in a bulge in the sphecical form ('bottom exposure). Other minor fluctuabions
in permeability are noted at this point but do not greatly affed bhe
genecal spherici'ty of the pattern.
A seemingly homogeneous sample of Fronbier Sandstone provides even a
more sbrrking example of ,this phenomena (see Plate 7). One immediately notes
the total indfffibiveness of bhe th~in laminae in deflectrng the isotropic form. In
repeated experiments on this un~t the effect was always the same. As the sample
is so nearly void of any indicat'ions of stratification when viewed with the
eye, one w6uld hardly exped obher than this type of result, but as it has been
demonstrated such expecrtakions are often unrewarded.
It should be noted rhat all the structural interfaces which exhibi,t controls
on rhe flood fronlt pa'ttern may not be expressed on the rad'iographs because of
the intensky of radi,ation used. Smimilarly, poorly developed structures wi,th little
contrast may not be noted if they are not perfedly aligned with the incoming
x-rays. Al'w anlobher control seldom deteded on radiographs is that of an isotropic
fabric. When such a fabric is strongly ~nfluenltial in vertical sections cut
parallel to the fabric man, then the major axis of an introduced fluid partern
will generally be inclrned to the stratification. In sections cut perpendicular
to the fabric mean, this incl'inaffion may be occasionalfy noticed but only in
stereo or dherwise it would appear parallel to the s,tratification planes.
An example approach,ing the non-deteated presence of a permeability control
is illust~ated rn a specimen of the Englevale Sandskone (Plate 8). As one
examines khe exposed area which is later accupled by the flooding fmnt, it
appears to be quitte homogeneous. The advancing finge,ring front, however,
quickly denotes a preferred drrection of advance which IS noted to sub-
parallel the distinct cross-lam~na~ions at the bottom of the sample. Thrs effect
bhen draws attention to the very faint trend's of stratification with'in the flmding
area seen in the right hand sets of the stereo pairs. Had the exposure pos~ition
of the right hand set been slightly different then the reasons for a preferred
direation of permeability would not have been so easily deduced. Nevertheless,
"hidden" stratification is again noted to develop a distinct control on flu~d
migration.
Cryptostructures are sum,marrly seen to act as barriers or condurts simlilar
bo many visrble structures when, and if, differences In effectrve porosrty exist
across them. If, however, no aggregate difference exists, fluid flow wrll not be
affected. There are several reasoas why structural rnterfaces may not affect fluid
flow :
(1) the accessory minerals, common consk~tuents of structural interfaces,
may have textures relat~vely close to the surrounding particles.
(2) if much smaller s~zed
clasts of accessory minerals are involved
then their increased angularity may counteract the effeobive-poros'ity re-
duckion expected from mixing grain srzes alo'ng the contact.

102 J. RAYMOND RUTLEDGE
(3) accessory minerals dended by x-rays m3ay be tco scattered along
structural planes and the immediate area of decreased permeability may
be surrounded and bypassed by the fluid and the effect go unnct~ced.
OBSERVATIONS OF FLUID PATTERNS IN PREWET'TED SAMPLES
Flow conditions were initiated in a number of prewetted specimens to
simulate more closely condlt~ons fcund In nature. The saturant fluid and the
Induced opaque fluid were In each case ml~scible. When prewetted fluid patterns
were compared to patterns produced In equivalent "dry" specimens, essentiallv
no differences were nclted in the manner of advance in three out of four
sandstone types. Note, for example, rhc similar~'ty of the tongued advance In
the dry and re-imbibed sample of Dakota Sandbstone of Plate 1, f~gure 4 and
Plate 2, figure 3. Low contrasts between the fluids are responsible for the poor
seprodu&~on of the picture on Plate 2 denoting - the prewetted front.
The prominemtly labated fronlt typica1,ly developed in dry specimens of the
well-laminated Tonganoxie Sandstone, howeve~r, was smoothed cut into a
diffused spher~cal shape during one series of Injections conduoted on a prewdted
sample (Plate 2, flg. 2). Durlng a rerun of th'is exper~ment on a new
speclmen of the same unit, relat'ively no dmiffusion occurred even bhough the
sample was shown to be well saturated. Because of these inconsistencies, it
would be prem,atuse to draw any definilte conclus~ons about these I~rnited otservations
without addit~onal work being conduoted in t,his area.
COMPARISON OF FLOOD FRONT PATTERNS TO FABRIC
A,ttempts to determine the aggregate fabric of previously injected specimens
with stemrad~ography were unsuccessful. Thmln slices three to four millimeters
in thickness were made from the specimens but proved to be too thick to
diisbinguish one individu'al grain from the superimposed Images of other grams
lying wiltlhln the same pllane. By makring much thinner slices the aggregate
fa4ric wculd not be evident and thin-section procedmures would have to be
instistuted. To be useful In fabric stud'ies radiography must be able to supplant
the tedious task of making numerous thin sect,ion, grain coun~ts and orientations.
CONCLUSIONS
Stereoradiography provides an excellent mahd to v~sually study natural
fluid flow condlil~ions on a small scale. The major advantage is tbat ilt offers
a bee-dimensional view of fluid interfaces within the structural framework of
a rock. This method is I~mited, however, by the small sample site suitable for
d i n g good radiograph's.
The effect of cryptostn~ctures of fluid movement appears to be largely de-
pendent upon effecjtive porosity. Like visible skructures, they act as hrriers or
ohannels when differences of permaability exist across them and exhibict
essentially no effect when the differences are insign~ficant or dispersed. Un-
expressed structural conlbrcl may therefore have a profound effect upon the
permeable potential of a sandstone unit.
ShMPLE LOCALITIES
(1) Baseline Sandstone--outcrop sample from vicinity south of Glendale Junction, Clark
Co.. Nevada.

RADIOGRAPHIC TECHNIQUES IN FLUID MIGRATION 103
(2) Beria Sandstone-cored sample from well in Illinois.
(3) Englevale Sandstone member of the Labette Shale-outcrop sample from T 26 S,
R 25 E, Bourbon Co., Kansas.
(4) Dakota Sandstone-outcrop sample 20 miles west of Salina, Saline Co., Kansas, on
Highway 40.
(5) Frontier Sandstone--outcrop sample three miles north of Vernal, Uintah Co., Utah,
on Highway 44.
(6) Illipah Sandstone-outcrop sample from Mt. Hamilton, White Pine Co., Nevada.
(7) Tonganoxie Sandstone--outcrop sample from Dietman Crossing, Douglas Co.,
Kansas.
(8) Unidentified Cretaceous Sandstone-outcrop sample from vicinity north of Judith
Mountains, Judith Basin Co., Montana.
(9) Unidentified Tertiary Sandstone--cored sample from Ventura Basin, California.
(10) Weber Sandstone--outcrop from Blue Mountain, Moffat Co., Colorado.
REFERENCES CITED
Chatenever, Alfred, 1951, Microscopic behavior of fluids in porous systems: Funda-
mental Research on Occurrence and Recovery of Petroleum 1950-51, American Petr.
Inst., Lord Baltimore Press, Baltimore, Md., p. 250-253.
Clauser, H. R., 1952, Practical Radiography for Industry: Reinhold Publishing Corp.,
New York, 301 p.
Eastman Kodak Company, X-Ray Division, 1957, Radiography in Modern Industry:
Rochester, N. Y., 122 p.
Fettke, C. R., 1938, The Bradford oil field: Pennsylvania Geol. Survey Bull. M-21, p.
211-228.
Fraser, H. J., 1935, Experimental study of the porosity and permeability of clastic
sediments: Jour. Geol., vol. 34, p. 910-980.
Gatton, L. C. and Fraser, H. J., 1935, Systematic packing of spheres with particular
relation to porosity and permeability: Jour. Geol., vol. 34, p. 980-1010.
Griffiths, J. C., 1949, Directional permeability and dimensional orientation in the
Bradford sand: Pennsylvania State College Mineral Industries Exp. Sta. Bull. 54,
p. 138-163.
---- and Rosenfeld, M.A., 1953, A further test of dimensional orientation of q u ~ z
grains in Bradford sand: Am. Jour. Science, vol. 251, p. 192-214.
Hamblin, W. K., 1962, X-ray radiography in the study of structures in homogeneous
sediments: Jour. Sed. Petrology, vol. 32, p. 201-210.
---- , 1965, Internal structures of "homogeneous" sandstones: Kansas State Geol.
Surv. Bull., 175, part I, p. 1-37.
---- and Salotti, C. A,, 1964, Stereoscopic radiography in the study of ore textures:
Am. Mineralogist, vol. 49, p. 17-29.
Hubbert, M. K., 1940, The theory of ground water motion: Jour. Geol., vol. 48, p.
785-944.
Hutta, J. J., 1956, Relation of dimensional orientation of quartz grains to directional
permeability in sandstones: unpub. M.S. thesis Pennsylvania State University.
King, F. H., 1899, Principles and conditions of the movements of ground water: U. S.
Geol. Surv. 19th Ann. Rept., p. 59-294.
Laird, A. D. K. and Putnam, J. A., 1951, Fluid saturation in porous media by x-ray
technique: Fundamental Research on Occurrence and Recovery of Petroleum 1950-51,
Am. Petroleum Inst., Lord Baltimore Press, Baltimore, Md., p. 240-249.
Lehr, J. G., 1961, Emperical studies of laminar flow in porous consolidated media:
Geol. Soc. America Abstracts, p. 93A.
Meinzer, 0. E. and Wenzel, L. K., 1942, Movement of ground water and its rela-
tion to head, permeability and storage: Hydrology, McGraw-Hill Book Co., New
York, 77 1 p.

104 J. RAYMOND RUTLEDGE
Muskat, Morris, 1937, The Flow of Homogeneous Fluids in Porous Media: McGraw-
Hill Book Co., New York, 763 p.
Potter, P. E. and Mast, R. F., 1963, Sedimentary structures, sand shape fabrics, and
permeability: Jour. Geol., vol. 71, part I, p. 441-471; part 11, p. 548-565.
Scheidegger, A. E., 1960, The physics of flow through porous media: Univ. of
Toronto Press, Toronto, Can., 313 p.
Slichter, C. S., 1899, Theoretical investigation of the motion of ground water: U. S.
Geol. Survey 19th Ann. Rept., part 11, p. 295-384.
Manuscript received July 28, 1966

Actinocoelia maeandrina Finks, from the Kaibab Limestone
of Northern Arizona
Brigham Young University
~es~~~c~.-Numerous sponges of the species, Arfinoroelia maeandrina Finks, are found
in cherty concretions of the Beta Member of the Kaibab Limestone. They were collected
from 8 sections in an east-west traverse, from the Kaibab Plateau on the east, to near
Las Vegas, on the west.
Although the sponges are numerous and occur over a wide area, only one species
was found in the member.
Associated fossils include brachiopods, pelecypods, crinoid stems, corals and bryozoa.
'IEXT
Page
Introduction ....................................... .I05
Acknowledgments ............................ 106
Description .......................................... 106
Available material ............................ 108
Repository ........................................ 108
References Cited .................................. 108
CONTENTS
INTRODUCTION
1LLUSTP.ATIONS
Plate page
1. Artinoroelia maeandrina
Finks ............ following page 108
Text-f igures
1. Index map of collecting
localities .................................... 106
2. Generalized stratigraphic
sections of collecting
localities .................................... I07
The Kaibab Formation, from which all fossils for hhis stuciy were oollected,
covers an area of many thousand s q u miles in northern Arizona, southern
Utah and southern Nevada. It extends from Snowflake, Arizona, in the southeast
to Spring Mountain, Nevada, on the west. To the north, it has been found
as far as the San Rafael Swell and bhe Confusion Range in Utah. Fmsils for this
work were not obtained from all extremifiies of the formahion, but were collected
from an eastward tnaverse from the Kaibab Plateau in north-central Anizona,
on ehe east, to an area near La Vegas on the west (Text-figure 1). McKe
(1938, p. 155) reported sponges from sectrons to the north and they have also
been reported by Finks (1960, p. 71-72) from the formatron.
The Kaibab Formation varies In th~cknm from place to place, but averages
approximately 400 feet in the Kailhb Plateau.
Because of the high structural posirt~on of the Kaibab Formation and h-
oause of ilts resistance to erosion, many areas have been expsed within the unit
fmm which sponges can be easllly collwted. Road cuts which pass through the
formation proved to be good areas.
McKee (1938, p. 45-54) divided the Kaibab Formation into two members.
The upper Alphla Member is composed of cherty beds of limestone, fine clastir
material, thin-bedded impure limestone, and gypstone, and the lower Beta Member
is composed of massive, cherty, fosuiliferous, normal marlne Ilmestone
(khleh, 1960, p. 1). The Beta Member oonta~ns the fossils described here. The
fossil sponges appear In bhe center of cheat concretions and nodules which are

abundant in the upper Beta beds, and have been referred to as the "cannon-
ball chert" (Schleh 1960, p. 44). These nodules are abundant and range in
diameter from two to ten inches, but average six inches. The size averages
somewhat larger in sou~hern Nevada bhan in northern Arizona.
The Alpha Member in many areas has been almost compl&ely erded away
m &at the Beta Mem'ber, and mnsequenltly the fossil sponge beds, is found on
or near bhe 'top i,n most exposures.
The Betia Member sbands as a resistant ledge and the less resistant overlying
Alpha Member, when present, camonly forms genitle slopes above.
Because of the resi-nt nature of the chert nodules and concretions, indivi-
dual fossil sponges are rarely weathered free of the matrix. Only in lhhe ZBS
Vegas area were fossil sponges found which were not entirely encased in this
cherty, limestone mterilal (Plate 1, fig. 3).
Acknowledgments
Financial support for collecting the sponges and for their laboratory study
was provided by an Undergraduate Research Pa&icipa+ion grant by rhe Natfiod
Science Foundabion to the Depantanent of hlogy, B~igham Young University.
Page charges were also covered by the grant. Dr. J. Keith Rigby made initial
aollections at two of ,the Imlities and aided he author in preparation of mate-
rials and the manuscript.
Description
These sponges occur as massive spheroidal forms which are generally flat-
tened on one side. Finks (1960, p. 72) attributes this flattening to the effect of

8
LAS
VEGAS
I I
KAIBAB LIMESTONE SPONGES 107
TOROWEAP
VALLEY
I I
4 1
HACKS
CANYON
KAlBAB
PLATEAU
I I I I
Limestone Shale Sandstone Chert Gypsum
0 100 200 300 Feet
1 1 1 1 1 I J
TEXT-FIGURE 2.-Generalized stratigraphic sections of collecting localities (modified from
McKee, 1938).
pout-bugid compa&ion. On those rare speolmens where weathering has left the
exterior exposed the sponge resembles a common household sponge. In most
oases the chertified interior can be observed only after cutting the spherical
nodules in which the sponges were encad.
The diameter of individual sponges ranges from 25 to 95 mrn. in eastern
collections (locations 1, 2, and 3, Text-fig. 1) but from 55 to 190 mm. in the
west (location 8). The thickness or height likewise Increases from 10 to 65 mm.
in eastern locations (locations 1, 2, and 3) to 35 to 135 mm. in western ones
(location 8). Although external measurements show an increase in size firom

108 LELAND R. GRIFFIN
east to west, there appears to be no noticeable change in the size of the internal
gtruatures In bhe same speci , lmens.
The canal system, which forms a rad~ating pattern throughout the sponge,
has ilts or~gin near the base. As @he cands are traced toward the surface Hhey are
usually straigh,t, but meandering and branching of the canals does appear at
vanious intervals. In cross section the canals may be oval ar round, but many
have ,irregular shapes. They emerge at bhe surface with ovt~a about the same
size as the associated canalls. Bemuse of bhe meandeming nature of the canals and
interventing trabeculae the surfiwe has a grooved appearance.
Width of canals ranges from 0.4 to 2.5 m., with 1.3 mm. king khe
average slze. Width of the canals stays approximately the same from their or~gin
unbil term~nabion at the surface.
The trabeculae are massive and form a radial pattern throughout the sponge
and are somewhat narrower bhan the associated canals. They have a thickness of
from 0.3 to 2.0 mm., with 1.0 mrn. being the average slze. The skeletal network
al'so has horizontal elements whah laterally connect the radiating major structures.
Presence of lateral trnberulae gives the network a meander~ng appearance.
Because of bhe chenb~fied nature of the sponges, the skeletal material has
been preserved to various degrees. In the Kaibab Plateau area (locations 1 and
2), spicules are best preserved but in hd~bies to the west only spicule fragments
are preserved or are ldi'ng all together.
Where present, bhe sp~cnles are irregularly arranged tetraclones, 0.2 to 0.3
rnm. long. The axes are 0.03 to 0.05 mm. thick, and the rays, which have
icregular &apes, are 0.02 to 0.04 rnm. tblck and 0.04 to 0.13 mm. long.
Most spimens have approximately khew same canal measurement, however,
trhere are individuals wh~h have a smaller than average size. These few
forms my mpresenlt a new species when the genus has been intently studied and
varitiabiilfity evaluated.
Avarlable Material.-Approximately 170 specimens were collected for the
~nvestlgabion, bat numerous &her examples were sstudsied in the field. Seveml
thousand sponges could be calleatd at each loca181ty with little difficulty had
vaniation warranted such exten~sive mte~li'al. Since only a s~ngle, moderately
variable species was d~iscovered, col~lmtions were not enlarged.
Repository.-The collmtion iss housed by the Department of Geology, Brigham
Young University. Figured specimens are numbers 1098, 1099, 1100; the
rernairrder are ca'hloped under the coller~ing locality numbers.
REFERENCES CITED
McKee, E. D., 1938, Environment and history of the Toroweap and Kaibab forma-
tions of Northern Arizona and Southern Utah; Carnegie Inst. Wash., Publ. 492,
Washington D.C., 268 p.
Shimer, H. W., 1919, Permo-Triassic of Northwestern Arizona; Bull. Geol. Soc.
Amer., v. 30, p. 476-478.
Reeside, J. B., Jr., and H. Bassler, 1922, Stratigraphic sections in Southwestern Utah
and Northwestern Arizona; U.S. Geol. SUN. Prof. Paper 129, 69 p.
Finks, R. M., 1960, Late Paleozoic Sponge Faunas of the Texas Region; Bull Amer.
Mus. Nat. Hist. v. 120, Article 1, New York, 160 p., 50 pls.
Schleh Edward E., 1960, (ms), Toroweap and Ka~bab Format~ons in a part of
Parashant Canyon, Mohave County, Arizona; unpublished master's thesis, University
of Kansas.
Manuscript rece~ved November 1, 1966

EXPLANATION OF PLATE 1
ACTINOCOELIA MAEANDRZNA FINKS
FIG. 1, 2.-Photomicrographs of tetraclonal spicules in coarse textured chalcedony; BYU,
1098, x85.
FIG. 3.-External view of weathered sponge; BYU, 1100, xl.
FIG. 4.-Polished transverse section through a lobate speclmen showing canals and
trabecular patterns; BYU, 1099, xl.

GRIFFIN PLATE 1
Actinocoelia maeandrina PINKS FROM THE KAIRAB LIMESTONE

Preliminary Petrology and Chemistry of Late
Cenozoic Basalts in the Western Grand
Canyon Region
Brigham Young University
ABSTRACT: Late Cenozoic basaltic volcanism in the western Grand Canyon region of
northwestern Arizona and adjoining Utah affords an opportunity to investigate the
interrelations of volcanism and concurrent vertical tectonic movements, the origin and
evolution of basaltic magmas, and the character of the upper mantle beneath an wolv-
ing plateau province. This paper presents preliminary data gained from a long-range
petrographic and chemical study of the basalts, the puropse of which is to provide some
answers to these fundamental geologic problems.
Although the lavas are all essentially alkali olivine basalts, considerable and
significant variations occur in their mineral and chemical composition, allowing dis-
crimination of at least six basalt-types. These types range from a mafic basalt rich in olivine
and clinopyroxene and having 45 wt. O/o silica to basalts carrying xenwrysts of com-
plexly zoned plagioclase and quartz with 52 wt. TO silica. Gamma-ray spectrometry dis-
closes certain types, including the most mafic basalts, contain as much as 1.5% K,
11 ppm Th, and 3 ppm U, whereas other types have much lower concentrations of
these heat-producing elements, near values for average worldwide alkali olivine basalts.
Ultramafic inclusions containing partially decomposed orthopyroxenes, as well as
clioopyroxine and olivine, are unique to the youngest basalt flows in the southeastern
part of the region. The lack of systematic chemical variations in the basalts as a func-
tion of time, together with basalt-types of similar age but greatly different compositions
adjacent to one another, indicates several primitive or parental magmas were involved.
CONTENTS
TEXT
page
Introduction .......................................... 1 10
Acknowledgments ................................ 11 1
Classification ....................................... .ll I
4. Th and K concentrations in
some basalts from the western
Grand Canyon region ................ 120
Plates
Petrography .......................................... 113
Segmiller Mountain type ................ 1 13
Middle flows above Cane Springs ..I13
1.
2.
Photomicrographs of basalts
........................ following page 112
Photomicrographs and com-
Poverty Mountain type .................... 11 5
Middleton type ................................ 11 5
Washington type ............................ 115
Cralg's Knoll type ............................ 1 17
Young Stage 111 flows .................... 117
Th, U, and K in the basalts ................ 118
Discussions and some tentative
conclusions ........................................ 12 1
References Cited .................................. 122
positional variations of plagioclase
xenocrysts in the Middleton
flow ........ following page 112
3. Photomicrographs of basalt
and untramafic inclusions
........................ following page 112
Tables
1. Optical and compositional data
on minerals in some basalts
ILLUSTRATIONS from the western Grand
Text-figures
1. The area of this report ............ 110
2. Distribution of basalts in the
western Grand Canyon region..ll2
2.
Canyon region ............................ 114
Chemical and normative compositions
of some basaltic rocks
from the western Grand
3. Th and U concentrations in
some basalts from the western
Grand Canyon region ................ 119
3.
Canyon region ............................ 116
Composition of clinopyroxene
from sample 8 ............................ 117

M. G. BEST, W. K. HAMBLIN, & W. H. BRIMHALL
TEXT-FIGURE I.-Stippled pattern covers the area of this report.
INTRODUCTION
Late Cenozoic basaltic volcanism in the western Colorado Plateaus was
recognized by Powell (1875) and Dutton (1882) in their surveys of the
region some 90 years ago. In su~bsequent investigations of the volcanic history
of southern Utah by Gregory (1950) and of northwestern Arizona by Colton
(1937) and Koons (1945) the basalts were considered in a geomorphic
context, serving perhaps as means to a better understanding of regional
geologic history. Current investigation by Hamblin (1963, and mr) indicates
at least 16 periods of extrusion, during which recurrent movement developed
along the major north-south normal faults marking the western margin of the
Colorado Plateaus province. The basalts, therefore, serve as valuable keys in
elucidating the history of tectonic movements and erosional processes in this
region during the Late Cenozoic.
In all these earlier investigations only slight passing attention has been
given to the mineralogy and chemistry of the basalts themselves, it being
thought that they are all of uniform dharacter, lacking any significant varia-
tions. In a preliminary petrographic examination of samples from the western
margin of the Colorado Plateaus (hereafter referred to as the western Grand
Canyon region, Text-fig. 1) it was indeed found that there is a uniformity
in mineralogy; all are essentially alkali olivine basalts, being composed simply
of plagioclase, Ca-rich clino-pyroxene, olivine, and Fe-Ti oxide. However,
conspicuous and fundamental variations appear in the compositions of each of
these minerals and as well in their modal proportions. Although less thman 100
samples have been examined thus far from the entire region, petrographic
types can be recognized having limits in both space and time.

CENOZOIC BASALTS 11 1
Chem~cal analysis for major elements in 3 samples and for Th, U, and K
in 40 others conflrms that the chemical variations suggested by petrographic
study are real and significant. For example, silica ranges frilm slightly under
45 wt. YO to slightly over 52 wt. 70. Th, U, and K concentrations range
from values below those for average, - worldwide alkali olivine basalt to
values among the highest known.
This paper 1s a progress report on a long-range petrological and chemical
investigation of the Late Cenozoic basalts in the western Grand Canyon region
wlth the intended aim of casting light on the related problems of tectonic
history and geophysical processes in the crust and upper mantle.
ACKNOWLEDGMENTS
Appreciation 1s expressed to J. A. S. Adam5 and Rice University for
their cooperatiion In @he determilnation of Th, U, and K in the samples while
W. H. Brimhall was on leave from Brigham Young University. J. Keith Rigby
provided helpful assistance on the project and criticism of the manuscript.
Expenses for f~eld work, thin sect~ons, and the four major element dhemical
analysis were defrayed by a Natronal Sc~ence Foundation grant GP-3923 to
W. K. Harnblin.
CLASSIFICATION
Hambl~in (1963, and ms) has established a chronol~grc grouping of
basaltic flows in the region based prirnariIy on the nature of the surface on
whidh they were deposited. The oldest lavas*, Stage I, were extruded onto
eroslon surfaces bearing no relation to the present dralnage system. They now
cap high level mesas. Lavas of intermediate age, Stage 11, were deposited on
surfaces which can be demonstrated to be ancestral to the present drainage
system. They occur on pediments, stream terraces, and on moderately 'high
mesas in the region. Classic Stage I1 lavas near St. George, Utah, have caused
development of inverted valleys; i.e., sinuous lava-capped mesas produced by
erosion of soft rock from around lava-frlled stream channels. Stage 111 lavas
are defined as those whrch have been extruded on erosion surfaces of the
present erosional system. Cinder cones are commonly associated with these
young flows. The generalized distrrbution of the basalts, arranged by stages,
IS shown in Text-fig. 2, together with pertinent geographrc names mentioned
in this paper.
Petrographic basalt-types recognized in this preliminary rnvestlgation on
the basis of mineralogical composition and certain textural features do not,
in every case, correspond to the grouping by stages explained above. In this
paper the basalts will be descrrbed in a petrographic context, rather than by
stages. Each basalt-type will bring together basalts having common petro-
graphic character~stics, the name for the type being drawn from a prominent
occurrence exemplifying the type, as follows:
Segm~ller Mountain Type
Middle flows above Cane Springs
Poverty Mountain Type
Middleton Type
*Although radiometric age dates on the basalts are pending, it is reasonable to expect
an early Pliocene or perhaps late Miocene age for the oldest lavas

112 M. G. BEST, W. K. HAMBLIN. & W. H. BRIMHALL
TEXT-FIGURE
2.-Distribution of basalts in the western Grand Canyon region, after
Hamblin (rns). SC, Santa Clara flow; MF, Middleton flow; BRP, Black Rock
Pass; SM, Segmiller Mountain; CS, Cane Springs; TH, The Hat; PM, Poverty
Mountain; MT, Mount Trumbull; ML, Mount Logan; VT, Vulcan's Throne; MD.
Mount Dellenbaugh.

PHOTOMICROGRAPHS OF BASALTS
FIG. 1.-Poverty Mountain type of basalt. Groundmass consists of minute granules of
colorless clinopyroxene and slightly larger olivines jacketed by dark hematitic
borders. The glomeroporphyritic clot (1.2 mm. in diameter) includes an
olivine wlth a dark alterat~on border, a fresh, pale green clinopyroxene, and
rather homogeneous bytownite subhedra.
FIG. 2.-Washington type of basalt. Slightly vesicular rock comprised of abundant
ol~vine, zoned, pale brown clinopyroxene, and equant Fe-Ti oxides with minor
amount of lathllke plagioclase. ol=olivine; cp=clinopyroxene. Photomicm-
graph is 1 mm. in length.
FIG. 3.-Segmlller Mountain type of basalt. Fine granules of ollvine and colorless
clinopyroxene crowd between laths of plagioclase. Fe-Ti oxide grains are
somewhat larger. Phenocrysts of olivlne (longer length of one in photo is
0 6 mm.) are scattered throughout the basalt.
FIG. 4.-Middleton type of basalt. Laths of plagioclase, barbed Fe-TI oxide, and
Irregular colorless clinopyroxene make up the groundmass. Microphenocrysts
of olivine occur elsewhere in the rock. Characteristic of this type of basalt
are xenocrysts of quartz, with reaction rims of fibrous pyroxene and brown
glass, and large, complexly zoned and ~nclusion-filled, probably xenocrystic,
grains of plagioclase Quartz xenocryst is 2 mm. long
PHOTOMICROGRAPHS AND COMPOSITIONAL VARIATIONS OF PLAGIOCLASE
XENOCRYSTS IN THE MIDDLETON FLOW
FIG. 1.-Variation of An content in an east-west traverse across the larger phenocryst.
Dotted portion of diagram Indicates extent of ~nclusion-rich zone in plagie
clase. Crossed nicols.
FIG. 2.-The outer margin of an anhedral xenocryst 5 mm. in diameter. Traverse indi-
cating varlatlon in An content runs east-west through twin lamellae (nearly
extinguished) from left-hand margin of photo. Crossed nicols
PHOTOMICROGRAPHS OF BASALT AND ULTRAMAFIC INCLUSION
FIG. 1.-Peridotlte inclusion from the Vulcan's Throne flow. Large olivine (ol),
clinopyroxene (cp) and orthopyroxene (op) grains are surrounded by a
flner aggregate of olivine, clinopyroxene, oxlde, and plagioclase. The dark
material around the orthopyroxenes was presumably formed by decomposition
of the orthopyroxene, which is unstable at atmospheric pressure in magmas of
the composition represented by the Vulcan's Throne flow. The photo is 5
mm. In length.
FIG. 2.-Santa Clara flow. Vesicular basalt containing fresh ollvlne phenocrysts set
in a matrix of plagioclase laths with granules of olivine, clinopyroxene, and
Fe-TI oxide. Some dark turbid glass is present; Photo is 2 mm. long.
FIG. 3 -Enlarged vlew of decomposition rim on orthopyroxene (near extinct~on posi-
tlon under crossed nlcols). Length of photo is 0.9 mm. The rim is a parallel
Intergrowth, parts of which are in optical continuity wlth one another and wlth
either the planar lamellae or the "granule" lamellae in the adjacent orthopyrox-
ene Optlcal identification of the phases in the intergrowth is difficult, but
clinopyroxene appears to be dominant.

PLATE 1
PHOTOMlCROGRAPHS OF BASALT
4
BEST, HAMBLIN, AND BRIMHALL

BEST, HAMBLIN, AND BRIMHALL PLATE 2
PLAGIOCLASE PHOTOMICROGRAPHS AND COMPOSITIONAL VARIATIONS
IN THE MWDLETON FLOW

PLATE 3 BEST, HAMBLIN, AND BRIMHAU
2 3
PHOTOMICROGRAPHS OF BASALT AND ULTRAMAFIC INCLUSION

Washington Type
Craig's Knoll Type
CENOZOIC BASALTS 113
In addition to these reiatlvely widespread basalt-types, there are samples of
rather unique Stage I11 lava flows not yet asv~gned to any type and which
w~ll be described separately. These flows are the Santa Clara and the Vulcan's
Throne. Further work now in progress may necessitate revision of the basalttypes
as conceived in this paper.
PETROGRAPHY
Segmdler Mounta~n type.-The most widspread basalt-type in the region
occurs as flows of Stage I west of the Grand Wash fault, in the northern part
of the Shivwits Plateau at Moqui Mtn. and Segmiller Mtn., and in the
Uinkaret Plateau at Mt. Trumbull and Mt. Logan. In hand specimen, this
rock type, here called the Segmiller Mountain type, is medium gray with conspicuous
small phenocrysts of olivine, generally showing marginal alteration to
red-brown Fe-oxide. In th>ln section, the texture is intergranular, less commonly
pilotaxitic. The principal constituent 1s slightly zoned andesine-labradorite.
A smoky green clinopymxene occurs as small aggregated granules between
the plagioclase laths and only very rarely as phenocrysts. Olivine occurs bath
as phenocrysts and as a groundmass constituent. Every sample has rndividual
and aggregated magnetite grains containing a small amount of (exsolved ?)
~lmenite. Apatite is present in mlnute amounts. A typical sample, 58, havlng
an average grain size IS shown in Plate 1, flg. 3. Optical data on constituent
minerals of the same sample are shown In Table 1.
1
~iddh jLbw.r &d~e Cane Spu~rzg~.-These flows consist of a thick sequence
of gray diabases of Skage I. Abundant fresh plagioclase, together with lesser
amounts of dark pyroxene and ollvine, the latter jacketed by orange-brown
oxide, can be seen in hand specimen. Angular vesicles comprise a few percent
by volume of samples from central portions of the flaws, whereas samples
from the exposed bases are scoriaceous and strongly oxidized. Aligned plagioclase
laths characterize many parts of the flows. Laced through the flows are
planar dikelets, 1-3 inches in width, superficially resembling the diabase but
consisting - of finer basaltic material with abundant rounded vesicles.
In thin section, rhe plagioclase in the diabase is found to be quite homogeneous
with only slight peripheral normal zoning. Dotted throughout the
mosaic of aligned plagioclase laths are large, pale brown anhedra of clinopyroxene
and a lesser quantity of peripherally oxidized olivlne. Some clinopyroxene
anhedra are aggregated together into clots 2-3 mm. in diameter.
Smaller clinopyroxenes, Interstitial to the laths of plagioclase as well as the
rims of large clinopyroxenes, are darker brown and have a lllac tint, indicating
enrichment in TiO,. Fe-TI oxides in the d~iabases are typically barbed rods
but some are irregular in outline, still fewer are cubic.
The basaltlc dikelets contain no olivine, the mafic minerals being a dark,
lilac-brown clinopyroxene, an oxide (approximately 15 modal %), and several
percent of acicular, very pale green amphi~bole of undetermlined character. The
plagioclase is An,,. It would appear that these dikelets represent late differentiated
liquids derived, perhaps by filter pressing, from the enclosing
diabase and injected along planes of weakness in the just crystallized parts

TABLE I
Optical & Compositional Data on Minerals in the Grand Canyon Basalts
Plagioclase' Clinopyroxene2 Olivine'
Sample mole % An 2v, mole % FO Location of Sample
Segmiller Mtn. Type
15A 5 3 52 74 middle flows (dlabase) Cane Springs
72
5 4
58
40 m 5 2
48 m 5 2
60 m
48 5 1
Poverty Mtn. Type
7 2
middle flows (basaltic dikelets) Cane Sprlngs
Mt. Logan
west base of Mt. Trumbull
west of Hurricane fault and Mt. Logan
25
24
73, 76, 79 p
45 m
53
79
west Poverty Mtn.
east central Shlvwlts Plateau
26 37 m 54 east central Shivw~ts Plateau
58-70 p
63 52 m
58-63 p
Middleton Type
54 Black Rock Pass
3
42
46 m
49 m
32-58 p
8 3
3 rn~les northwest of St. George
Middleton flow along highway east of St George
Washinglon Type
8 51-GO4
Crarg's Knoll Type
8 6' east central Moqui Mtn.
north Moqui Mtn.
68 45 m
Santa Clara Flow
875
4 825 head of Santa Clara flow along Highway
5 48 m absent
Young Stage 111 flow on Uinkaret Plateau
78 toe of Santa Clara flow south of Highway 91
30 85' flow beneath Vulcan's Throne
3 7
57
42
47
m
m
50 85
78'
east of Hurricane fault, 8 miles north of state line.
cascade (?) on southeast s~de of Mt. Trumbull
'The number indicated for microlltes (m) was derived from the maxlmum extlnctlon angle in sections I to (010) using the high tempera-
ture curve of Troger (1959, p. 111); that for phenocrysts (p) was obtained by the bisectrix method using the high temperature
curves of Troger (1959, p. 101) or by the universal stage using curves of Slemmans (1962).
'2V, was measured by direct rotation between two axes oa the universal stage; precision lo.
3Measured by the X-ray method of Yoder and Sahama (1957); precision < 1%.
'Rims have values in the low SO'S, the cores in the high 50's. Analyzed sample was concentrate of core material.

CENOZOIC BASALTS 115
of the flows. Kuno (1965) reached similar conclusions on other basaltic
dikelets.
Poverty Mountain type.-Available samples from the southern part of the
Shivwits Plateau plus samples from the flows at Black Rock Pass and at
"The Hat" are of a type resemb1,ing the Segmiller Mountain type. They are
called the Poverty Mountain type and occur as both Stage I and I1 flows. The
groundmass is similar to the Segmiller type but in addition to ubiquitous
phenocrysts of marginally decomposed olivine there are scattered phenocrysts of
euhedral to subhedral labradori'te-bytowniIte and Ca-rich clinopyroxene, (Plate
1, fig. 1). Weak oscillatory zoning is evident in some plagioclases; the
pyroxenes are pale green, some very weakly zoned to darker rims, and com-
monly seived with groundmass material. Glorneroporphyr~tic clots up to 2.5
mm. i,n diameter of pyroxenes and plagioclases are characteristic of this rock
type
Middleton type.-Cerbain classic Sage I1 flows occurring as invetted valleys in
the St. George Basin, plus the Stage I1 Pintura flows northeast of Hurricane,
may be designated as the Middleton type. These flows are characterized by
phenocrysts of complexly zoned plagioclase as much as 1 cm. long and con-
stituting up to abut 10% of the rock. The euhedral to subhedral crystals
have a clear but narrow calcic rim enclosing an extensive area, quite sodic in
composition, generally rounded in outline, and pervasively riddled with dusty
opaque particles or matrix material in a crude mesh pattern. Inside this zone
of inclusions there is, in some phenocrysts, a clear core of similar composition
or one zoned towards more calcir compositions. The nature of this complex
zoning is portrayed by the universal-stage data in Plate 2. These phenocrysts
are remarkably similar to those from lavas of the San Juan Mountains illus-
trated by Larsen et aJ. (1938, especially figs. 15b, 16a, b) which were inter-
preted by them as xenocrystic. It is certain that at least some time during the
magmatic history of the Middleton-type flows, these complex phenocrysts
experienced resorption in the melt. Following partial resorption, magmatic
conditions shifted, possibly upon extrusion of the lava, and the thin dear
rim formed on the partially resorbed grains. In add'ition to xenocrystic plagio-
clase, some samples include 1 to 2% of glassy quartz xenocrysts--embayed
and jacketed by brown glass and aggregated acicular cl~nopyroxene. Olivine is
sparse. Pale green to brown clinopyroxene occurs mainly in the groundmass,
although phenocrysts are common; a few have seived cores and one instance
was found where such grains were clustered around an embayed xenocryst of
hypersthene.
A chemical analysis of the sample from the Middleton flow, Table 2
(see also Plate 1, fig. 4) discloses the presence of considerable silica such that
quartz is abundant in the norm. Fe is abundant compared to Mg. The felds-
pathic character of the rock is attested by the presence of 63% feldspar in
ihe norm.
Washzjzgton type.-Unusually mafic basalts constitute the Washington flow
(a classic Stage I1 inverted valley flow), a dike and associated small flow
remnant 8 m~les due south of Hurricane, and a flow on a small flanking
terrace on the east side of Moqui Mountain. The latter two occurrences are
possibly Stage I1 but accurate geomorphic classification is difficult. In hand

SiOr
TiOI
AI,O:,
FeO,
FeO
MnO
MgO
CaO
BaO
SrO
NarO
K,O
H20'
P,o5
TOTAL
S.I.*
D.I.
M. G. BEST, W. K. HAMBLIN, & W. H. BRIMHALL
TABLE 2
Chemical & Normative Compositions of Some Basaltic Rocks
from the western Grand Canyon region (A. G. Loomis, analyst)
8 4 2 4
Stage 11 (2) Stage I1 Stage 111
Washington type Middleton type Santa Clara flow
MgO x 100
*s.I. = -- wt. yo; D. I. - 2: normative kalsilite,
MgO + FeO + FerOl + NarO + KzO
nepheline, leucite, albite, orthoclase, quartz in wt. CJo
specimen, the rock, designated as the Washington type, is a dense black
aphanite dotted with small dark phenocrysts. Locally, the rock disintegrates
into polyhedrons one or two centimeters in diameter.
Under the rnicroscc~pe it is found that clinopyroxene and olivine comprise
more than half the rock, the olivine occurring as euhedral phenocrysts up to
2 mm. long and the pyroxene as somewhat smaller and less abundant pheno-
crysts and as an important groundmass constituent. The pyroxene is prismatic,
having moderate dispersion and a stronger brown color on the margins than
the cores. Chemical analysis of a concenkrate of khe lighter colored cores dis-
closes (Table 3) the pyroxene is an augite with a high content of MgO and
A120,. The remainder of the groundmass of this rock consists of a turbid
material containing obvious cubic magnetite, some of rather large site, and
minute laths of plagioc-lase, too small for optical determination of their
composition (Plate 1, fig. 2).

Fez03
FeO
MnO
MRO
CaO
Na20
K2O
P205
CENOZOIC BASALTS
TABLE 3
Composition of Cl~nopyroxene from sample 8 (A. G. Loomis, analyst).
wt. % numbers of atoms per 6 0
TOTAL 100.38 Ca 36.5%; Mg 52.9%, Fetz + Fe+3 + M n 10 6%
A chemical analysis and a normative calculation of the sample from Moqui
Mountain (Table 2) reveal the mafic character of this rock type; abundant
aikal~es and low silica being reflected in the appearance of over 7% orthoclase
and 6% nepheline in the norm.
Craig's K12011 ~ype.-These basaks, named from a hill 5 miles north of Mt.
Trurnbnll, are essentially plag~oclase-rich variants of the Washington type,
the textures and optical properties of other constituents being similar. It is
found as the earher Sbage I11 flows on the Uinbaret Plateau, the "A" and
"B" flows of McKee and Schenk (1942) in ancestral Toroweap Valley, the
basal flow at Prospect Point across the Colorado River from Toroweap Valley,
most of the ~ntra-canyon flow remnants in the canyon of the Colorado River
from Prospect Point to Lake Mead, at Volcano Mountain west of Hurricane,
and in the northern part of Moqu~ Mountain.
Young Stuge III flows.-Available samples of the young Stage 111 basalts in
the region are generally hypocrystall~ne, the glass be~ng pradlcally opaque
because of abundant Fe-ox~de part~cles. Glassy, l~ght green olivine 1s common,
bath as phenocrysts and in the groundmass. Pyroxenes, restricted to khe
groundmass, are pale brown and pr~smatic.
One of the youngest Stage 111 flows-the Santa Clara northwest of St.
George-has been ~hemically analyzed (see Table 2); it has a moderate
amount of SIO,, high FeO and A1,0,, but K,O is low compared to the other
basalts in the region (see also data in the next sect~on). A photomicrograph of
this basalt is shown in Plate 3, fig. 2.
Young Stage 111 flows on the Uinkaret Plateau-the lava cascade associated
with the cinder cone d Mt. Trumbull md the Vulcan's Throne flows-are

118 M G. BEST, W. K. HAMBLIN, & W. H. BRIMHALL
unlque basalts in the entlre western Grand Canyon region because they contain
rather abundant clots or inclusions of aggregated olrvine and pyroxene. Blocks
of similar aggregates lie scattered upon the slopes of Vulcan's 'I'hrone. Most
inclusions are olivine-rich peridotite In which the olivines are coated with
brick-red Fe-oxide. Dark green, olivine-bearing pyroxenites are less abundant,
as are single, isolated anhedral crystals of jet black clinopyroxene up to 3 cm.
~n drameter (in the Vulcan's Throne flows). The texture ln the peridotltes and
pyroxenites is typrcally xenomorphic, veinlets of basaltic material commonly
permeate the pyroxenites along gram margins. Olivines are rich in the forsterite
end-member (95% for inclusions in Vulcan's Throne flows and 97% for a
blwk from the cone). Clinopyroxene (2V, 55") and orthopyroxene seem
about equally abundant In the pyroxenite lncluslons but orthopyroxene IS
-.
domlnanst or exclusrve in perrd&i,te.
Exsolution lamellae parallel to (100) are very weak in orthopyroxene of
peridot~te but strong In both pyroxenes of pyroxen~iltes. Clinopyroxene grains
tend to be smaller than the amoeba-like ortho~vroxenes. some of which ranee
~ ~
I I '7
up to 2 cm. and enclose the smaller olivines and clinopyroxenes. Orthopyroxenes
show weak to strong pleochroism. Deep brown splnel was noted in
mridotites. The network of basaltic mater~al rn the inclusions is no: entrrelv
related to physical entrance of host magma into a disintegrating rnclusion.
Much IS related to chemlcal breakdown of the orthopyroxesne, for these
grarns have conspicuous reaction rims of granular or aggregated acicular
clinopyroxene (?) (Plate 3, figs. 1 & 3). Plagioclase and olivine may also
be a by-product of this reaction but further work is necessary before its exact
nature is known.
'I%, U, AND K IN THE BASALTS
Forty samples of basalt representing ehe major types of the regron have
been analyzed for Th, U, and K by Willis Brimhall using a gamma-ray
spectrometer at Rice Unlverslty. Variance of these elements, horizontally and
laterally, within a single flow was not investigated in detail in thls prelrminary
survey; however, analysis of 13 samples from 4 localities in rhe Santa Clara
flow ylelded standard deviations of 0.32 ppm, 0.11 ppm, and 0.05 ppm
(207'0, 25%, and 11%) for Th, U, and K, respectively.
Four replicate analyses on a single sample of the Craig's Knoll type
showed the analytrcal precision (as standard deviations) is 0.22 ppm, 0.23
ppm, 0.03 ppm (376, 12%, and 3%) for Th, U, and K, respectively. If the
"within-flow" variance and the analytical precision are compared to analyses
on 28 other basalt flows, based on single analysis on a single sample, it rs
apparent (Text-figs. 3 & 4) that substantial variations in Th, U, and K occur
on the scale of the region. Assuming rhat the Individual analyses of flows
plotted in Text-Figs. 3 & 4 are representative, one may make the following
conclusions :
(1) There is a fairly consistent grouping of flows of a particular petro-
graphic rock type, the major exception being the Craig's Knoll type,
3 analyses of which are widely scattered.
(2) All of the analyzed samples from the Grand Canyon region are
richer in Th, U, and K than the worldwide average of tholeiitic basalts
and most are richer than average alkali olivine basalts (averages from

I PM M pr2i~
CENOZOIC BASALTS
SC Sonto Cloro
VT ~ulcon's Throne
A'
SM
CK
W
Craig's Knoll
Washington
M Middleton
PM Poverty Mountoin
SM Segrniller Mountain
A average alkali
olivrne bosalt
T overoge tholeiite
TEXT-FIGURE
3.-Th and U concentrat~ons In some basalts from the western Grand
Canyon region. The line represents the mean U/Th ratio for Hawaiian basaltic
rocks (after Heier et al., 1964, Fig. 3). Data for average (worldwide) basalts are
from Tatsumoto et al., (1965).

-
-
-
M. G. BEST. W. K. HAMBLIN. & W. H BRIMHALL
G K
SC Santa Clara
VT Vulcan's Throne
Gl' Gra~g's Knoll
W Washington
M Middleton
VT PM Poverty Mountain
SM Segmiller Mountam
A average alkali
W olivine basalt
W
W T average thole~~te
W
I I
TEXT-FIGURE
4.-Th and K concentrations In some basalts from the western Grand
Canyon region. The line represents the mean K/Th ratlo for Hawallan basalt~c
rocks (after Heier et al., 1964, Fig. 1). Data for average (worldwide) basalts are
from Tatsumoto PI al. (1965)

CENOZOIC BASALTS 121
Tatsurnoto et al., 1965). The Santa Clara flow is particularly low in
these heat-producing elements, whereas other late Stage I11 flows in the
sou~hern part of the region have very haigh concentrahons of Th and U.
The relatively mafic, silica-poor Washington type also has high concentrations
of Th and U.
(3) The coherence of Th, U, and K, noted by Heier et al. (1964) in
Hawaiian and other basalts holds true for Th-U but not for Th-K or
U-K in the Grand Canyon basalts. Larger values of Th or U do not
correspond with larger values of K in ehe Washington and Craig's
Knoll types and Vulcan's Throne flow. (If ~t were not for the mafic
basalbs, mostly of &age I but al'w the Washington flow (11) , and m e
of Stage I11 near Mt. Tmmbull, the coherence would be much better.)
The coherence in the Th-U (i.e., the Th/U ratio) for the Grand Canyon
basal'bs is displaced on,ly slightmly (0.5 ppm) toward higher U values, compared
to the Japanese and Hawaiian values (Heier et al., 1964), shown
by the diagonal line in Text-figs. 3 & 4.
(4) Heier et dl. (1964, p. 256) conclude that "the concentrations of
thorium, uranium and potassium increase with petrogenic evolution,
and the relative enrichment is rhoriurn>uranium>potassium." Taking
the three Grand Canyon basalts analyzed for major elements (Table 2)
as an example, the sequence of evolving magmas would be according to
samples 4, 42, and 8. Yet, the age relations are the reverse of th~is
sequence. Consideration of other criteria, the differentiation index
- (D. I. Z normative quartz, albite, orthoclase, leucite, kalsilite, and
nepheline; Thornton and Tuttle, 1960) and the solidification index
(S.I. = MgO X 100 / MgO + FeO + Fe,O, + Na,O + K20 in
wt. %; Kuno, 1965) i,ndicates the sequence of evolution from primitive
to differentiated magma should be 8, 4, and 42. Here, again, the age
relations are scrambled. The only conclusion which can be drawn from
the meager data at th~s pint is that the Grand Canyon lavas d ~d not all
evolve from some single, primitive parent, nor is there necessarily a
genetic relationship between many of the lavas. A more extended program
of sampling and analyses is clearly needed.
DISCUSSION & SOME TENTATIVE CONCLUSIONS
Basalt is the sole igneous rock-type exposed in the western Grand Canyon
region; only to the north are other types-the sllicic volcanlcs of the Great
Basin and High Plateaus of Utah-found along with basalt. Mineralogically
the basalts are fairly uniform, l.e., ubiquitous olivine, plagioclase, Fe-Ti oxide
and Ca-r~ch clinopyroxene and lack of Ca-poor pyroxene, yet rhe proportions
of the mineral cons.tituents are variable and the chem~cal compositions of
bulk basalt range from just ultrabasic (sample 8) to just ~ntermediate (sample
42). Sample 8 has nephellne and sample 42 quartz in the norms. These
mineralogical and chemical variat~ons appear to occur relative to both space
and time in the region.
It is apparent from the httle data now available that differentiation of a
single parent magma cannot explain all the observed co~mpositional variations.
It 1s more logical to consider the existence of several types of parent magmas
from which the observed lavas were derived and likely differentiated to some

122 M G. BEST, W. K. HAMBLIN, & W. H. BRIMHALL
extent. One might, for example, postulate that the Washington type of lava
was such a pr~mitlve magma, yielding, perhaps the Craig's KnolI type. The
Segmiller type migh,t have yielded differentiates of the Poverty Mountain type.
The Santa Clara flow w~th ~ts remarkably low concentrations of Th, U, and
K would appear to represent st111 another prim~tlve magma.
The actual development of these parent and primit~ve magmas must 11e
within the upper mantle and ~t IS an intriguing problem of fundamental con-
cern to petrology as to how comps~tionally different magmas are produced
TWO especially Interesting problems concern the orlgln of the inclusions
of peridotite and pyroxenlte in bhe Vulcan's Throne flow and xenocrysts of
quartz and plagioclase in Middleton type flows.
It m~ght be supposed that the inclusions represent accumulations of phenocrysts
In the coollng lava. However, the flow lacks phenocrysts of any type
of pyroxene, thus implylng some other mode of ongln. The presence of
partially resorbed orthopyroxenes in the ~nclus~ons suggests that at least that
phase was unstable in the magmatlc environment just prior to sulid~flcat~on of
the lava. Ultramafic ~nclusions have convembionally been Interpreted as fragments
from the upper mantle, caught up in the ascending magma. However,
recent invest~gations (see for example, Kushiro, 1965; Kuno, 1964; Talbot,
et dl., 1963) have suggested the alternate possibility that at h~gh pressures,
such as prevailing in the upper mantle and deep crust, phases prec~p~tating from
basaltic magma are of a d~fferent nature than those precipltatlng near surface
In simple basalt systems, Ne-Fo-SiO, and Di-Fo-En, increasing pressure causes
the lrquidus boundary between Fo and En to sh~ft toward Si0,-poor compositions.
Thus, an alkali ollvine basalt In which, at atmospheric pressure, Capoor
pyroxene is unstable, could, at high pressure, crystallize it stably Such
Ca-poor onth~p~mxenes brought from depth could exh,~bbt resorption relations
In surface lavas If this argument is to be applied to the ~nclus~ons at Vulcan's
Throne, one must also account for the presence of abundant Ca-rich clinopyroxene
along with the resorbed orthopyroxene. Another unexplained point
concerns the black cllnopyroxenes occurring as single large crystals In the lava,
which are different from the green ones In the inclus~ons.
It mlgh't seem reasonable to suppose that the xenocrysts In the M~ddleton
flows were der~ved from crustal rock bordering the volcan~c condu~t and Incorporated
Into the ascendllng m,agma. The fact that other nearby basalts (VIZ.
hhe Santa Clara), or for that mlatter, the basallts throughout the reglon, lack
xenocrysts could be explained, possibly, on the basis of a hlgher vrscos'ity of
the feldspaih~c magmas, retarding the rate at which forelgn material was completely
assimilated. Or, special cclnditions, such as very rap~d ascent to the surface
af,ter picking up the xenocrysts might have prevailed for these lavas and
none others. The nearby Plne Valley Mountaln body, along the marglns of
which the Mid'dleton type flows emanated, and prox~mate silic~c ashflow tuffs
may have supplied the pl~agimlase, quartz, and orthopyroxene occurring as xenocrysts.
Alternately, the xenocrysts rnl~ght have originated at high pressures where
a sh~ft in liquidus boundar~es allowed orthopyroxene, a sodlc plagioclase, and
possibly even quartz to precipitate.
REFERENCES CITED
Colton, H. S. 1937, The basaltic cinder cones and lava flows of the San Francisco
Mountam volcanic fleld, Arizona: Mus. North. Ar~z Bull., no 10. 49 p.

CENOZOIC BASALTS 123
Dutton, E., 1882, Tertlary history of the Grand Canyon district U.S. Geol. Surv.
Mon. 2, 264 p.
Gregory, H. E., 1950, Geology and geography of the Zion Park region, Utah and
Arizona: U.S. Geol. Surv. Prof. Paper 220, 200 p.
Hamblin, W. K, 1963, Late Cenozoic basalts of the St. George Basin, Utah: Interm.
Asscx. Petrol. Geol. 12th AM. Field Conf., p. 84-89.
---- , ms., Late Cenozo~c tectonic and volcanic history of the western Grand Canyon
region manuscript ln preparation.
Heier, K. S., McDougall, I., and Adams, J. A. S., 1964, Thorium, uranium, and
potassium concentratlorn in Hawaiian lavas. Nature, v. 201, p. 254-256.
Koons. E. D., 1945, Geology of the Uinkaret Plateau, northern Arizona: Geol. Soc.
Amer. Bull., v. 56, p. 151-180
Kuno, H., 1964, Alurn~nian augite and bronzite in alkall olivine basalt from Takasima,
North Kyusyu, Japan: In Advancing Frontiers in Geology and Geophysics
(Krishnan Vol.), Indian Geophys. Union, p. 205-220.
---- , 1965, Fractionation trends of basalt magmas in lava flows: Jour Petrol., v.
6, p 302-321.
Kushiro, I., 1965, The liquidus relations ~n the systems forsterite - CaA1,SiOe -
silica and forsterlte - nepheline - silica at hlgh pressures: Ann. Rpt. Geophys.
Lab., Carn. Inst. Wash. Yrb. 64, p. 103-109.
Larsen, E. S., Irving, J., Gonyer, F. A,, and Larsen, E. S., 3rd, 1938, Petrologic results
of a study of the minerals from the Tertiary volcanic rocks of the San Juan region,
Colorado; plagioclases. Arner. Min., v. 23, p. 227-257.
McKee, E. D., and Schenk, E. T., 1942, The Lower Canyon lavas and related features
at Toroweap in Grand Canyon: Jour Geomorph., v. 5, p. 243-273.
Powell, J. W., 1875, Exploration of the Colorado Rlver of the West: Washington,
D. C., Govt. Printing Office, 291 p.
Slemmorn, D. B., 1962, Determination of volcanic and plutonic plagioclases using a
three-or four-axis universal stage: Geol. Soc. Amer. Spec. Pap. 69, 64 p.
Talbot, J. L., Hobbs, B. E., Wilshire, H.G., and Sweatman, T. R., 1963, Xenoliths
and xenocrysts from lavas of the Kerguelen Archipelago: Amer. Min., v. 48, p.
159-179.
Tatsumoto, M., Hedge, C. E., and Engel, A. E. J., 1965, Potassium, rubidium, strontium,
thorium, uranium, and the ratio of strontium-87 to strontium-86 in oceamic
tholeiitic basalt: Sci , v. 150, p. 886-888.
Thornton, C. P., and Tuttle, 0. F., 1960, Chemistry of igneous rocks I, d~fferentiation
index: Amer. Jour. Sci., v. 258, p. 664-684.
Troger, W. E., 1959, Optixhe Bestimmung der gesteinbildenden Minerale, Teil I:
Stuttgart, E. Schwlezerbart'sche Verlagsbuchhandlung, 147 p.
Yoder, H. S., Jr., and Sahama, T., 1957, Olivine X-ray determinative curve: Amer.
Min., v. 42, p. 475-591.
Manuscript received November 4, 1966

PUBLICATIONS AND MAPS OF THE GEOLOGY DEPARTMENT
Brigham Young University, Research Studies,
Geology Serzes
Available numbers at $2.00 each
VOLUME 1, 1954
*Clark, Davld L., Stratigraphy and sedimentation of the Gardner Formation in Central
Utah, No. 1, 60 p.
*Hamblin, William Kenneth, Geology -. and ground - water of northern Davis County. - - Utah.
No. 2, 51 p., map.
*Murphy, Don R., Fauna of the Morrowan rocks of Central Utah, No. 3, 64 p.
*Knight, Lester L., A preliminary heavy mlneral study of the Ferron Sandstone. No. 4,
31 p.
*Dearden, Melvin O., Geology of the Central Boulter Mountains area, Utah. No. 5, 85 p.,
map.
VOLUME 2, 1955
*Perkins, Richard F., Structure and stratigraphy of the lower American Fork Canyon-
Mahogany Mountain area, Utah County, Utah. No. 1, 38 p., map.
*Olsen, Ben L., Geology of Baldy area, west slope of Mount Timpanogos, Utah County,
Utah. No. 2, 30 p., map.
*McFarland, Carl R., Geology of the West Canyon area, northwestern Utah County,
Utah. No. 3, 21 p., map.
*Rhodes, James A., Stratigraphy and structural geology of the Buckley Mountain area,
south-central Wasatch Mountains, Utah. No. 4, 57 p., map.
*McFarlane, James J., Silurian strata of the eastern Great Basin, No. 5, 53 p.
*Livingstone, Vaughn E., Jr., Sedimentation and stratigraphy of the Humbug Formation
in Central Utah. No. 6, 60 p.
VOLUME 3, 1956
*Croft, Mack G.. Geology -. of the northern Onaqui Mountains, Tooele County. . Utah. No.
I,' 44 p., map.
*Demars, Lorenzo C., Geology of the northern part of Dry Mountain, southern Wasatch
Mountains, Utah. No. 2, 49 p., map.
*Petersen, Morris S., Devonian strata of central Utah. No. 3, 37 p.
*Peterson, Deverl J., Stratigraphy and structure of the West Loafer Mountain, upper
Payson Canyon area, Utah Coun , Utah. No. 4, 40 p., map.
*Davis, Del E., A taxonomic study orthe Mississippian corals of central Utah. No. 5, 49
P.
*Stewart, Donald G., General geology, channeling, and uranium mineralization, Triassic
Shinarump Conglomerate, Circle Cliffs, Utah. No. 6, 38 p., map.
*Smith, Cleon V., Geology of the North Canyon area, Southern Wasatch Mountains,
Utah. No. 7, 32 p., map.
VOLUME 4, 1957
*Maxfield, E. Blair, Sedimentation and stratigraphy of the Morrowan Series In Central
Utah. No. 1, 46 p.
*Rawson, Richard R., Geology of the southern part of the Spanish Fork Peak Quad-
rangle, Utah. No. 2, 33 p., map.
*Cline, Charles W., Stratigraphy of Douglas Creek Member, Green River Formation,
Piceance Creek Basin, Colorado. No. 3, 46 p.
*P~tcher, Grant G., Geology of the Jordan Narrows Quadrangle. No. 4, 46 p., map.
*Erickson, Einar C., Geology and uranium mineralization in the East Gas Hills, Wye
ming. No. 5, 50 p., map.
*Rhodes, Howard S., The Mississippian System of Southern Alberta, Canada. No. 6, 67 p.
*Out of print but available on microfilm for $2.50 per number or $5 00 per volume.

VOLUME 5, 1958
*Harris, DeVerle, The geology of Dutch Peak area, Sheeprock Range, Tooele County,
Utah. No. 1, 82 p., map.
*Prescott, Max W., Geology of the northwest quarter of the Soldier Summit Quadrangle,
Utah. No. 2, 44 p., map.
*Bullock, Reuben L., The geology of the Lehi Quadrangle, Utah. No 3, 59 p., map
*Thomas, Glenn H., The geology of Ind~an Springs Quadrangle, Tooele and Juab
counties, Utah. No. 4, 35 p., map.
*Henderson, Gerald V., Geology of the northeast quarter of Soldier Summit Quadrangle,
Utah. No. 5, 40 p., map.
*Bentley, Craig B., Upper Cambr~an stratigraphy of Western Utah No. 6, 70 p
*Moyle, Richard W., Paleoecology -. of the Manning Canyon Shale In Central Utah. No
7, 86 p.
*Zeller, Ronald P., Paleoecology of the Long Trail Shale Member of the Great Blue
Limestone Oqu~rrh Range, Utah. No.8, 36 p.
VOLUME 6. 1959
*Powell, D. Keith, The geology of southern House Range, M~llard County, Utah. No.
1, 49 p., map.
*Davis, Briant L. Petrology and petrography of the Igneous rocks of the Stansbury
Mountains, Tooele County, Utah. No. 2, 56 p.
*Crosby, Gary W., Geology of the South Pavant Range, Mrllard and Sevier counties,
Utah. No. 3, 59 p., map.
*Foster, John M., Geology of the Bismark Peak area, North Tintic D~str~ct, Utah County.
Utah. No 4, 95 p.; -map.
*Gould, Wilburn J., Geology of the northern Needle Range, M~llard County, Utah.
No. 5, 47 p., map.
*Johnson, Kenneth D., Structure and stratigraphy of the Mount Nebo-Salt Creek area,
Utah, No. 6, 49 p., map.
*Berge, Donald L., Intrusive and metamorphic rocks of the Silver Lake Flat area, American
Fork Canyon, Utah No. 7, 46 p, map.
VOLUME 7, I960
*Larsen, Norbert W., Geology and ground water resources of Northern Cedar Valley.
Utah County, Utah. No. 1, 42 p., map.
*Foutz, Dell R., Geology of the Wash Canyon area, southern Wasatch Mounta~ns, Utah.
No. 2, 37 p., map.
*Robinson, R~chard A.. Some Dresbachian and Franconian trilobites of western Utah.
No. 3, 59 P.
*Kennedy, Richard R, Geology between Prne (Bullion) Creek and Tennirle Creek, eastern
Tushar Range, P~ute County, Utah. No. 4, 58 p., map.
*Berge, John S., Stratigraphy of the Ferguson Mountain Area. Elko County, Nevada. No.
5. 63 P.. map.
*Berg, Charles W, Heavy mineral study of the intrus~ve bod~es of the central Wasatch
Range, Utah. No. 6, 31 p., map.
*P~tcher, Max G., Fusul~n~ds of the Cache Creek Group, St~kine R~ver area. Cassiar
District, British Columbia, Canada. No. 7, 64 p.
Brigham Young University Geology Studies
VOLUME 8, 1961
$3.50
Mollazal, Yazdan, Petrology and petrography of Ely limestone in part of Eastern Great
Basin, p. 3-35, 4 pls.
Beach, Gary A., Late Devonian and Early Mississippian biostratigraphy of Central Utah,
p. 37-54, 2 pls.
Slade, M. Lyle, Pennsylvanian and Permian fusulinids of the Ferguson Mountain area.
Elko County, Nevada, p. 55-92, 10 pls.
*Out of print but available on microfilm for $2.50 per number or $5 00 per volume.

Robinson, Gerald B., Jr., Stratigraphy and Leonardlan fusulinid paleontology in central
Pequop Mountains, Elko County, Nevada, p. 93-145,4 pls.
Wright, Richard E., Strahgraphic and tectonic interpretation of Oquirrh Formation, Stans-
bury Mountains, Utah, p. 147-166.
Hodgkinson, Kenneth A,, Permian Stratigraphy of northeastern Nwada and northwestern
Utah, p. 167-196.
VOLUME 9, 1962
Part 1
$2.00
Geology of the Southelti Wasatch Mounrarns and V~cinity, Utah. A Symposium.
Hintze, Lehi F., Precambrian and Lower Paleozoic Rocks of North Central Utah, p. 8-16.
Rigby, J. Keith and Clark, David L, Devonian and Mississippian Systems in Central
Utah. p. 17-25.
Blssell, Harold J., Pennsylvanian-Permian Oquirrh Basin of Utah, p. 26-49.
Hardy, Clyde T., Mesozoic and Cenozoic Stratigraphy of North-central Utah, p. 50-64.
Phillips, Wllliam R., Igneous Rocks of North-central Utah, p. 65-69.
Hintze, Lehi F., Structure of the Southern Wasatch Mountains and Vicinity, Utah, p. 70-
79, 1 PI.
Rigby, J. Keith, Some Geornorphic Features of the Southern Wasatch Mountalns and
Adjacent Areas, p. 80-84, 1 pl.
Bullock, Kenneth C., Economic Geology of North-central Utah, p. 85-94.
Hintze, Lehl F., Geologic map of area (two color, 20" x 32").
Part 2
$4.00
Willes, S. B, The mineral alteration products of the Keetley-Kamas area, Utah, p. 3-28,
map.
Baer, J. L., Geology of the Star Range, Beaver County, Utah, p. 29-52, map.
Swensen, A. J., Anisoceratidae and Harnitidae (Ammonoidea) from the Cretaceous of
Texas and Utah, p. 53-82.
Tidwell, W. D., An Early Pennsylvanian flora from the Manning Canyon Shale, Utah, p.
83-101.
Clark, D. L., and Ethington, R. L., Survey of Permian conodonts in western North America,
p. 102-114.
Hanks, K. L., Geology of the central House Range area, Millard County, Utah, p. 115-
136, map.
Hanks, T. L., Geology and coal deposits, Ragged-Chair Mountain area, Pitkin and
Gunnison counties, Colorado, p. 137-160, map.
Rigby, J. Kelth, Current research in the Department of Geology, Brigham Young Uni-
versity, p. 161-162.
VOLUME 10, 1963
$4.00
Ash, S. R., Bibliography and index of Conodonts, 1959-1963, p. 3-50.
Wells, R B., Orthoquartzites of the Oquirrh Formation, p. 51-81.
Prince, D., Mlsslsslppian coal cyclothems In the Mannlng Canyon Shale of Central
Utah, p. 83-103.
Brimhall, W. H., Progress report on Selenium in the Manning Canyon Shale, Central
Utah, p. 104-120.
Kaufmann, H., Some monocllnlc Amph~boles and relation of their physical properties
to chemical composition and crystal structure, p. 121-158.
VOLUME 11, 1964
$3 00
Elake, J. W., Geology of the Bald Mountains intrusive, Ruby Mountains, Nevada, p. 3-35.
Markland, T. R., Subsurface water geology of Spanish Fork Quadrangle, Utah County,
Utah, p 37-65.
John, E. C., Petrology and petrography of the Intrusive igneous rocks of the Levan area,
Juab County, Utah, D. 67-96.

Fowkes, E. J., Pegmatites of Granite Peak Mountain, Tooele County, Utah, p. 97-127.
Schneider, M. C., Geology of the Pavant Mountains west of Richfield, Sevier County,
Utah, 129-1 39
VOLUME 12, 1965
$4.00
Brady, M. J., Thrusting in the Southern Wasatch Mountains, Utah, p. 3-54.
Black, B. A., Nebo Overthrust, Southern Wasatch Mountains, Utah, p. 55-90.
Bordlne, B. W., Paleoecologic implications of Strontium, Calcium, and Magnesium in
Jurassic rocks near Thistle, Utah, p. 91-120.
Bullock, L. R., Paleoecology of the Twin Creek Limestone in the Thistle, Utah area, p.
121-148
Lufkin, J. L., Geology of the Stockton stock and related intrusives, Tooele County, Utah,
p. 149-164.
Rigby, J. K., Stratigraphy and Porifera of Ordovician rocks near Columbia Icefields, Jasper
National Park, Alberta, Canada, p. 165-184.
Ethington, R. L., and Clark, D. L., Lower Ordovlc~an conodonts and other m~crofossils
from the Columbia Icefields section, Alberta, Canada, p. 185-206.
VOLUME 13, 1966
$4.00
Rigby, J. K., and McIntlre, W.G., The Isla de Lobos and assoc~ated reefs, Veracruz,
Mex~co, p. 3-46, 8 pls., 9 text-figs.
Chamberlalo, C. K., Some Octocorallia of Isla de Lobos, Veracruz, Mex~co, p 47-54, 2
pls., 1 text-fig.
Jensen, J. A., Dinosaur eggs from the Upper Cretaceous North Horn Formation of
Central Utah, p 55-67, 4 pls., 2 text-f~gs
Stelninger, R., Geology of the Kingsley Mlning Dlstrlct, Elko County, Nevada, p. 69-88.
4 pls , 5 text-f~gs.
Rutledge, J. R., A study of fluid migration In porous medla by stereoscopic radlograph~c
techn~ques, p. 89-104, 8 pls., 1 text-f~g.
Gnffin, L. R., Artrnocoelza mrreandrina Finks, from the Ka~bab Limestone of northern
Arlzona, p. 105-108, 1 pl.. 2 text-figs.
Best, M. G., Hamblln, W. K., and Brimhall, W H., Preliminary petrology and chemistry
of Late Cenozoic basalts In the western Grand Canyon region, p. 109-123, 3 pls.,
4 text-flgs.
Maps
Physiographic map of Utah by J. K. Rlgby, Black and wh~te, 8#" x 11" ............ $ .lo
Geolog~c map of Utah by L. F. Hintze, 1959, 8%" x 11" ........................................ .15
Preliminary geologic map of the House Range, Millard County, Utah, by L F.
Hintze, 1959, scale 1" equals 3,850 ft., ozalid print IS 36" x 48" ................ 2.00
Preliminary geologic map of the Cr~cket Mountains, Millard County, Utah, by
L. F. Hintze, 1959, scale 1" equals 4,000 ft., ozalid print 36" x 48" ............ 2.00
Preliminary geologic map of the Northern Wah Wah Range, Millard County,
Utah, by L. F. Hintze, 1960, scale 1" equals 4,000 ft., ozalid print is 32"
x 40" ...................................................................................................................... 2 00
l'rellminary geologic map of the Burbank Hills and Northern Needle Range,
Millard County, Utah, by L. F. Hintze, 1960, scale 1" equals 4,000 ft.,
ozalid print .......................................................................................................... 2 00
Cieology of the southern Wasatch Mountains and v~cinity, by L. F Hintze
(from Vol. 9, Pt. 1) two colors 20" x 32" .................................................... 100